US1984060A

US1984060A - Telephone system

Info

Publication number: US1984060A
Application number: US609570A
Authority: US
Inventors: Deakin Gerald; Hatton William
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1931-08-11
Filing date: 1932-05-06
Publication date: 1934-12-11
Anticipated expiration: 1951-12-11

Description

Dec. H, 1934. G. DEAKiN El AL TELEPHONE SYSTEM Filed May 6, 1932 2 Sheets-Sheet 1 FIG. 3

FIG?

2 J i /a //v VENTORS G DEA/(IN W. HATTO/V [WWW/g -ATTORNEY Dec. 11, 1934. DEAK|N r AL 1,984,060

TELEPHONE SYSTEM Filed May 6, 1932 2 Sheets-Sheet 2 FIG. 4 g? 052 cs3 l 'O-UQ-"W NATEGINHL 3/4 RE G/S TEF-SENDER G. DEA/(IN INVENTORS m HATTON A TTORNEY Patented Dec. 11, 1934 UNITE srrss PATENT OFFICE TELEPHONE SYSTEM Application May 6, 1932, Serial No. 609,570 In France August 11, 1931 23 Claims. (01. 179-18) This invention relates to telephone systems and more particularly to automatic and semi-automatic telephone systems in which line finder switches are employed for establishing connection with calling lines.

The object of this invention is to minimize the equipment required for handling originating calls and to provide a more emcient switching arrangement in such systems.

Heretofore it has been economically impracticable to provide a sufficient number of line finder switches to care for all calls without delay in the busy periods. According to this invention an arrangement is provided whereby a no-delay service is obtained with a minimum number of switches. To this end, a number of finders in a group of primary line finder switches are reserved for peak load conditions and are automatically brought into service when all or nearly all of the regular line finders are busy. Each of the regular line finders is directly connected with a selector switch but the overfiow line finders are arranged to extend a connection over one of a group of secondary finders, each of the secondary finders being directly connected with aselector switch. The secondary finders and associated first selectors are common to a plurality of groups of primary line finders, the secondary finders having access to all of the overflow finders of these groups. When all or nearly all of 'the regular line finders are busy, the secondary finders are adapted to hunt for an overflow line finder switch which has access to the calling line. The overflow line finders are identical in construction and interchangeable in service with the regular line finders. The selectors are also identical in construction and operation irrespective of whether they are individual to normally used line finders or individual to secondary finders.

Another feature of the invention is a control relay common to the regular line finders of a group which includes one or more overflow line finders, the operation of the control relay when one or more of the regular line finders are avail able being effective to prevent the operation of any of the overflow line finders. When there are no regular line finders available, or only a few of finders available, the control relay remains normal thereby enabling operation of a group of secondary finders to seize an idle overflow line for use in extending the calling line to a selector switch.

The invention will be better understood by considering a telephone system in which the features of this invention are embodied. One such system is illustrated in the drawings and will be described in detail insofar as such a description tends to explain the features of the invention. The invention is not limited in its use to the system illustrated but may be applied in any telephone system which employs line finder switches for extending calling lines.

Referring to the drawings:

Fig. 1 shows a diagrammatical layout of the system embodying the invention;

Fig. 2 shows a subscribers station A and a line finder switch LF;

Fig. 3 shows a secondary finder switch OF having access to finder switches such as LF; and

Fig. 4 shows a group selector GSl which may be 15 individual to a regular line finder such as LF or individual to a secondary finder such as OF; it also shows brushes and terminals representing an intermediate selector G82 and a final selector G33, and shows a called subscribers station E.

Referring now to Fig. 1, S1, S2 and S3 represent subscribers stations; LFl and LF2 represent normally employed primary line finders in a group having access to the same subscribers lines; GS1a and GS1'b represent group selectors in- 25 dividual to the finders LFl and LF2, respectively; ELF represents an extra or overflow finder which has access to the same group of lines as the finders LFl and LF'2 but which is not used for extending a calling line until all or nearly all of the 30 normally employed primary line finders are busy; OFl and .OF2 represent secondary finders which have access to the overflow finders of two or -more groups of primary line finders (only one such groupbeing shown); GS1c and GSl d 35 represent group selectors individual to the secondary finders CPI and OF2, respectively; G52 and G83 represent intermediate and final selectors required for completing the extension of a connection to a desired line; LC represents link 40 circuits individual, respectively, to the group selectors; RG represents a register sender for receiving dial impulses from a calling subscribers station and for controlling the extension of the connection by the group, intermediate and final 45 selectors to a wantedline, and R0 represents switching means for associating an idle register sender with a group selector.

Upon origination of a call and if not less than a certain number of the normally employed line 59 finders are idle, the connection is extended by one of the normal finders such as LFl or LFZ to the associated link circuit LC and thence to a register sender RG which will control the extension of the connection by the group selector GSl-a, 55

or GS1-b as the case may be and by an intermediate selector such as G62 and a final selector such as G83 to the called line.

If, however, less than a certain number of the normal finders in the group are idle when a call is initiated, a plurality of secondary finders such as OFl and OF2 will be caused to hunt for one of the overflow finders such as ELF having access to the calling line. The arrangement may be such that the overflow finders do not respond to the initiation of a call unless all of the normally employed finders are busy.

The circuits of this system are so defined that all of the primary line finder switches both normal and overflow may be exactly similar, the normally used finders being permanently connected to first selector switches and the overflow finders to terminals in the banks of secondary finders. All of the group selector switches may also be exactly similar, the normally used selectors being each permanently associated with normally used primary line finders and the overflow selectors with secondary finders; so, that, by means of this arrangement, any finder switch may be arranged to work with any group selector switch regardless of whether the connection is made directly or through a secondary finder switch.

The finder switch LF shown in Fig. 2 may, therefore, represent either a norma ly used finder or an overflow finder, and the group selector G81 shown in Fig. 4 may either be considered as individual to a normally used finder or be considered individual to a secondary finder such as OF shown in Fig. 3.

Although the finder and selector switches may be of any type usually employed in such systems, the finder shown in Figs. 2 and 3 are of the single-motion type having two sets of brushes displaced 180. The finder LF comprises the operating magnet 110 and the brushes numbered 111 to 115 inclusive; the finder OF comprises the operating magnet 210 and brushes numbered 211 to 217 inclusive. The selector switches G81, G62 and G83 shown in Fig. 4: are

of the revertively controlled type, a registersender being employed on each call to receive the dial impulses and thereupon control the selective operations of these switches. The selector G81 includes the brushes 310, the

operating magnets

311 and 312, relays numbered 313 to 317 inclusive and a sequence switch of the well known rotary type having a plurality of cams used for controlling the sequence of the various switching operations incidental to the operation of the selector; the sequence switch comprises a magnet 320 and cams numbered 321 to 339 inclusive.

The extension of a connection under normal conditions will now be described, the line finder LP of Fig. 2 being considered one of the normally used finders and connected directly to the link circuit and group selector GSl shown in Fig. l. When the subscriber at station A removes the receiver to originate a call, the line relay 101 operates in a circuit from battery through the winding of relay 101, right hand contact of cutoff relay 102, over the line 100, and back to ground at the left hand contact of relay 102. Relay 101 closes a circuit for operating the group relay 107. Relay 107 functions as a start relay for all of the normally used line finders of the group having access to the line and has individual contacts for initiating the operation of each of these normally used line finders.

Group relays

107 and 108 together control the start relay 202 which is associated with the secondary finders having access to the overflow finders of this primary group. The circuit for starting the operation of the finder LF may be traced from ground through the winding of marginal relay 108, inner right hand front contact of relay 107, over conductor 106 in Fig. 2 and over conductor 306 in Fig. 4, through the lower springs of sequence switch earn 327, the back contact of relay 313, the inner lower back contact of relay 315, the lower left hand and upper right hand springs of cam 329, over conductor 307, and through the stepping magnet 110 of line finder LP to battery. Similar circuits are closed through the wind-ng of relay 108, other front contacts of relay 107, and the stepping magnets of all other idle normally used line finders of the group. Since relay 107 has no contacts for connecting the winding of relay 108 to selectors associated with secondary finders, relay 108 is operatively unafiected by the busy or idle condition of these selectors and their associated secondary finder switches. Relay 108 may be adjusted so that the current through its winding is sufficient to cause its opeartion only when more than a predetermined number of the normally employed selectors and primary line finders are idle. Should it be desirable to employ the overflow finders only when all of the normally employed selectors and primary line finders are busy, relay 108 will not require a marginal adjustment since the sequence switches of all of these selectors will have been advanced out of their normal position. Several of the normally employed line finders being idle, the marginal relay 108 operates in series with the stepping magnets of the free line finders. Relay 108 thereby prevents the operation of relay 202 which controls the starting of the overfiow finders. As soon as the brushes of one of the hunting line finders engages the terminals of the calling line, a circuit is completed from battery through the winding of resistance 119 and the left hand front contact of relay 101 over conductor and through brush 115 of finder LF in Fig. 2, over conductor 305 in Fig. 4, through the upper left hand and lower right hand springs of sequence switch cam 326, and through the lower winding of relay 313 to ground. Relay 313 operates and closes a circuit for operating the marginal relay 314; this circuit may be traced from battery through resistance 119, the left front contact of relay 101, conductor 105, conductor 305, the upper springs of sequence switch cam 326, the upper winding of relay 313, the lower winding of relay 314, the upper springs of sequence switch cam 328, the front contact of relay 313, the lower springs of cam 327, over conductor 306, inner right hand front contact of relay 107, and through the winding of the marginal relay 108 to ground. The closing of this circuit serves to make the terminals of line 100 test busy to other hunting line finders, to hold relay 313 operated, and to operate the marginal relay 314. Relay 313 also opens the circuit for operating the magnet 110 of the line finder LF, thus stopping the brushes 111 to 115 inclusive on the terminals associated with the calling line. The operation of relay 314 closes a circuit from ground through its front contact, the upper right hand and lower left hand springs of sequence switch cam 325, and through the winding of relay 315 to battery. Relay 315 operates in this circuit, looks through its inner upper front contact and the lower springs of sequence switch cam 339, and closes a circuit from ground through the lower front contact of relay 315, the springs of sequence switch cam 337, winding of relay 317, over sleeve conductor 303,

1 net of each of these finders.

1*,98Qoa0:

through brush 1'13. of line: finder LE5 conductor" 1'03, and winding of: cut-ofl: relay? 102 to battery. The cut-oil. relay 1102: and; the. sleeve relay'31i7 arethereby operated m series; Relay'l02 disconnects:

the line relay 101. from. the conductors: of line: and relay 317-: extends. the connection from. the line 100. through brushes: 111 and 112,; over" conductors 301- and 302;. through the: upper left hand and lower right hand springs: of: sequence. switch cams 332: and: 333,. and. through thewindeings of answering supervisory-relay 3-16-tozground and battery respectively; Relay 31-6; is: thereby operated to close a circuit for operating. the sequence switch magnet 320 to advance the sequence switch from itsnormal position; this circuit is traced from ground at the left hand front contact ofv relay 316-, upperleft hand spring-of. sequence switch cam. 322; over conductor 318,.and through the winding. of magnet320 to. battery. The operation of the sequence switch and other. link circuit equipment of group'selector G81- exa tends the connection from line; 100' to: an idle register-sender which receives the impulses ere-- ated by the operation. of the calling subscribers dial. These operationsof the'group selector G81 and register-sender and the selecting operations of the switches GSlI, G82 and (3513- form. no part of the present. invention and. will not, therefore, be described hereina.

The extension of aconnection at a time when. there are no'noi'mallyemployedfinders available, or when there are less. than a given. number. of normally employed line finders available,. will. now be considered.v In this case the linefinder LE of Fig. 2. is considered as one; of the overflow finders which terminates:- in the banks of sec.- ondary finders such. as the. finder. OE shown in. Fig. 3, and the groupselector. GSl. isconsidered as being individual to the. secondary finder OF of Fig. 3. The secondary finder OF hasaccess: to the overflow findersof several. primary line finder groups, the line finder LF representing an. overfiow finder of one of the primary line finder groups. The overflow finders (not shown) of. the other primary line finder groups are also connected to terminals in the banks. of secondary, finder OF and other similar secondary finders. When the line relay 1.9.1 operates, it causes. the. operation of the group. relay 107 as hereinbefore described, but since there are av limited number of regular line finders. idle the current through the winding of. the. marginal relay 10.8 (in series with the operating magnets of. the idle regular finders) will be insufficient. to cause its opera tion. With relay 107. operatedandrelay 10.8.nor. mal, a circuit is: closed from. ground. through the left hand front contact of relay 107, back. contact of relay 1108, conductor. 120 to battery through the winding of the start relay 202 which is associated withv all the secondary. finders-having access to the overflow finder LF' and other overfiow finders of the same primary line finder group. Although not shown, it is understood that there is a similar start relay such as relay 202 for. each mi.-

1 mary line finder group, to the overflow finders. of.

which, the group of secondary findershas access. Relay 202 connects battery through: resistance. 200 to terminals in the banks of the secondaryv finders having access to the overflow finders such. as LF, there being a set of contactsv of. relay 202 for each of these overflow finders. Relay 202' also closes an obvious circuit for operatingrelay 207. Relay 287 is common to all the secondary finders and has a contact for operating the'driving mag- The circuit for.

operating: the magnet: 210 of. the finder OF is traced. from. battery through the winding of this magnet, the inner front contact of relay 207, and. through. the back contact of relay 209 to ground.v There is a relay similar. to relay 209 for each of the secondary finders for stopping the movement of the finder brushes as soon. as they cngagethe-contacts of: the overfiow line finder LF. Assuming that the secondary finder OF is the one. which first finds an idle one of the overflow finders and that this overflow finder is the finder LP, a circuit is closed from battery through resistance 200, the left inner front contact of relay 202, brush 217 of the finder OF, through the right hand winding of relay 209 to ground. Theoperation of relay 209 connects its left hand winding in series with the winding of relay 208, in. parallel with the right hand winding of relay 20.9; thereby reducing the potential at brush 217 to serve: as a busy condition to prevent other secondary finders from seizing the same overflow finder. Relay 208- operates thereby connecting ground to conductor 306 to cause the operation of magnet 110 of the overflow finder LF in the same manner as hereinbefore described. The overflow finder LF now operates in precisely the same manner as that hereinbefore described, when no secondary finder was used, with the exception that the circuits over conductors 301 to. 305 inclusive now include the brushes 211 to 215 inclusive of the finder OF as well as the brushes 111 to 115 of the finder LF.

It. is thus seen that the same line finder circuit may be used either to-work direct with a group-selector. such as shown in Fig. 4 or with a secondary finder such as is shown in- Fig. 3. Hence the samecircuit can be used for any of the line finders regardless of whether they are to be used for normal trafiic or whether they are to be. reserved for peakv load conditions, this advantage also extending tothe use of similar selector circuits. irrespective of whether they are individual to-normally employed line finders or individuaL to. the secondary finders.

What. is. claimed. is:

1.. In a telephone system, lines, a plurality of line finders for usein extending calls from said lines, overflow linefinders for use in extending calls from said. lines whenv a'predeterinined num ber of. said plurality of findersare busy, secondary finders for use in selecting an overflow line finder which has access to the line over which a call is being originated, and. first selectors one for each of said plurality of finders and one for each of said secondary finders.

2. Ina telephone system, lines, selectors for use in extending connectionsbetween said lines, regular line finders each permanently associated withand individual. to one oi said selectors, overfiow line finders. identical in construction with said regular. line finders and having access to the same. linesas said regular line finders, and secondary finders each permanently associated with and individual to one of said selectors, said secondary finders being operative when a predetermined number of said regular line finders are busy to select an overflow line finder which has access to' the line over which a call is being originated.

3; In a telephone system, lines, a plurality of line finders for use in extending calls from said lines, certain-of said line finders being reserved for useiun'der peakload'conditions, and means for preventing; the operation of said certain line finders as: long as; more than a predetermined number of said other line finders remain idle.

4. In a telephone system, lines, a group of line finder switches includingnormally employed line finders and reserve line finders, secondary finders having access to said reserve line finders, group selectors one for each of said normally employed line finders and one for each of said secondary finders, and means effective when all of said normally employed line finders are busy for initiating the operation of said secondary finders to select an idle reserve line finder for establishing connection with the calling line.

5. In a telephone system. lines, a group of line finder switches including normally employed line finders and reserve line finders, secondary find ers having access to said reserve line finders, group selectors, one for each of said normally employed line finders and one for each of said secondary finders, and means effective when less than a predetermined number of said normally employed line finders are idle for initiating the operation of said secondary finders to select an idle reserve line finder for establishing connection with the calling line.

6. In a telephone system, lines, a group of line finder switches including normally employed line finders and reserve line finders, secondary finders having access to said reserve line finders, group selectors one for each of said normally employed line finders and one for each of said secondary finders, and means for preventing the operation of said reserve line finders as long as more than a predetermined number of said normally employed line finders remain idle.

7. In a telephone system, lines, a group of line finder switches including normally employed line finders and reserve line finders, secondary finders having access to said reserve line finders, group selectors one for each of said normally employed line finders and one for each of said secondary finders, and means for preventing the operation of said reserve line finders as long as any of said normally employed line finders remain idle.

8. In a telephone system, lines, a group of line finder switches including normally employed line finders and reserve line finders, secondary finders having access to said reserve line finders, group selectors one for each of said normally employed line finders and one for each of said secondary finders, and means efiective Whenever there are only a predetermined minimum number of said normally employed line finders remaining idle for automatically bringing said reserve line finders into use.

9. In a telephone system, groups of lines, corresponding groups of primary line finder switches, each group including one or more finders reserved for use under peak load conditions, a group of secondary finders having access to the reserve finders of each of said primary line finder groups, selectors, one for each of the normally employed primary line finders and one for each of said secondary finders, and means efiective Whenever there is a predetermined minimum number of said normally employed primary line finders remaining idle in a group for automatically bringing the reserve finders of said group into use.

10. In a telephone system, groups of lines, corresponding groups of primary line finder switches, each group including one or more finders reserved for use under peak load conditions, a group of secondary finders having access to the reserve finders of each of said primary line finder groups, selectors, one for each of the normally employed primary line finders and one for each of said secondary finders, group relays one for each of said primary groups, means responsive to the initiation of a call over one of said lines for operating the group relay of the corresponding line finder group, means including said operated group relay for initiating the operation of all of the normally employed line finders in said primary group to hunt for the calling line, a control relay for each primary line finder group operative upon the initiation of a call over a line in the corresponding line group providing there are more than a predetermined minimum number of line finders in said primary group then idle for preventing the operation of the reserve finders of said primary group, and means including said control relay for automatically bringing said reserve finders into use whenever the number of normally employed line finders remaining idle at the time of the initiation or" a call does not exceed said predetermined minimum number.

11. In a telephone system, groups of lines, corresponding groups of primary line finder switches, each primary group including one or more switches reserved for use under peak load conditions, a group of secondary finders having access to the reserve switches of said primary line finder groups, selectors, one for each of the normally employed primary line finders and one for each of said secondary finders, means for operating the idle normally employed line finders in a group responsive to the initiation of a call over a line in the corresponding line group, means effective providing there are more than a predetermined number of normally employed primary line finders idle at the time a call is initiated in the corresponding line group for preventing the operation of said secondary finders, and means effective providing there are not more than a predetermined number of normally employed primary line finders idle at the time a call is initiated in the corresponding line group for operating the idle secondary finders to seize an idle one of the reserve finders of said primary group.

12. In a telephone system, groups of lines, groups of primary line finders, each group including one or more overflow finders reserved for peak load conditions, a group of secondary finders having access to the overflow line finders in each of said primary groups, selectors, one for each of said primary line finders exclusive of said overfiow finders and one for each of said secondary finders, start relays for said secondary finders, one for each of said primary groups and operative upon initiation of a call in the corresponding line group providing there are not more than a predetermined number of normally employed primary line finders then idle, means including contacts of an operated one of said start relays f or marking the terminals of the reserve finders of the corresponding primary group in the banks of said secondary finders, and a secondary group relay operatively controlled by each of said start relays for initiatinfl. the operation of said secondary finders.

13. In a telephone system, a group of lines, a group of primary line finders having access to said lines, some of said primary line finders being reserved for use as overflow finders, secondary finders having access to said overflow primary finders, selectors, each of said primary finders other than the overflow finders and each of said secondary finders being individual to a difierent one of said selectors, and means for preventing the operation of said overflow finders if more cues goeo than a fixed numberofsaid primary line finders other than the overflow finders are idle,

l l. Ina telephone system, a group of lines, line finders having access to said lines, some of said line finders being adapted forruse at all times, one or more of said line findersbeing adapted for use only as overflow finders, means responsive to the origination of a call over any one of said lines for initiating the operation of all idle finders exclusive of the overflow finders, and means efiective if more than a predetermined number of said finders other than the overflow finders are idle for preventing the operation or" said overflow finders. 7

15. In a telephone system, a group of lines, line finders having access to said lines, some of said line finders being adapted for use at all times, one or more of said line finders being adapted for use only as overflow finders, means responsive to the origination of a call over any one of said lines for initiating the operation of all idle finders exclusive of the overflow finders, means eflfective if more than a predetermined number of said finders other than the overflow finders are idle for preventing the operation of said overflow finders, and means effective if the number of said finders other than the overflow finders does not exceed said predetermined number for bringing said overflow finders into use.

16. In a telephone system, a plurality of primary line finders including normally employed finders and overflow finders, a group of lines col nected to the terminal bank of each of said plurality of line finders, secondary find-ers, said overflow finders being connected to terminals in the banks of said secondary finders, selectors, each selector being individual to one of said primary finders exclusive of said overflow finders or to one of said secondary finders, means efie'ctive upon the origination of a call over one of said lines for starting the operation of all idle normally employed finders in search for the calling line, and means effective when more than a predetermined minimum number of said normally employed primary finders are idle for preventing the operation of said secondary finders.

1'7. In a telephone system, a plurality of primary line finders including normally employed finders and overflow finders, a group of lines connected to the terminal bank of each of said plurality of line finders, secondary finders, said overflow finders being connected to terminals in the banks of said secondary finders, selectors, each selector being individual to one of said primary finders exclusive of said overflow finders or to one of said secondary finders, means efiective upon the origination of a call over one of said lines for starting the operation or all idle normally employed finders in search for the calling line, and means efiective when less than a predetermined minimum number of normally employed primary finders are idle for initiating the' operation of all of said secondary finders which are not in use.

18. In a telephone system, a plurality of primary line finders including normally employed finders and overflow finders, a group of lines connected to the terminal bank of each of said plurality of line finders, secondary finders, said overflow finders being connected to terminals in the banks of said secondary finders, selectors, each' selector being individual to one of said primary finders exclusive of said overflow finders or to one of said secondary finders, means effective upon the origination of a call over one of said lines for starting the operation of all idle normally employed finders in search for the calling line, means eiTective when a predetermined number of said normally employed primary finders are idlQ'fOI' preventing the operation of said secondary finders, and means efiective when less than said predetermined number of said normally em-- ployed primary finders are idle for initiating the operation of all of said secondary finders which are not in use. 7

19. In a telephone system, subscribers lines, a group of said lines, primary line finders each having access to the lines of said group, certain of said primary line finders being reserved for useunder peak-load conditions, secondary finders having access to said reserve primary finders, selectors for completing calls between calling and called lines, each selector being permanently associated with a single one of said primary finders exclusive of said reserve finders or with a single one of said secondary finders, means effective upon the origination of a call over any of the lines of said group for initiating the operation of all primary finders exclusive of said reserve finders which are associated with selectors not in use, and means effective only when less than a predetermined number of said primary finders exclusive of said reserve finders are idle for initiating the operation of said secondary finders in search for idle reserve finders.

20. In a telephone system, subscribers lines, a group of said lines, primary line finders each having access to the lines of said group, certain of said primary line finders being reserved for use under peak-load conditions, secondary finders having access to said reserve primary finders, selectors for completing calls between calling and called lines, each selector being permanently associated with a single one of said primary finders exclusive of said reserve finders or with a single one of said secondary finders, means effective upon the origination of a call over any of the lines of said group for initiating the operation of all primary finders exclusive of said reserve finders which are associated with selectors not in use, means effective only when less than a predetermined number of said primary finders exclusive of said reserve finders are idle for initiating the operation of said secondary finders in search for idle reserve finders, and means for causing the operation of a reserve finder when seized by a secondary finder.

21. In a telephone system, subscribers lines, a group of said lines, primary line finders each having access to the lines of said group, certain of said primary finders being reserved for use as overflow finders, secondary finders having access to said overflow primary finders, selectors for completing calls between calling and called lines, each selector being individual to a different one of said primary finders other than the overflow finders or to a diiferent one of said secondary finders, a relay common to said group of lines, means responsive to the origination of a call over any of said lines for closing a circuit through the winding of said relay and each of the selectors which are individual to primary finders and not in use, said relay being marginal so as to operate only when more than a predetermined number of said primary finders exclusive of said overflow finders are idle, and means controlled by said relay for initiating the operation of said secondary finders.

22. In a telephone system, subscribers lines divided into groups,- a group of primary line finders for each group of lines, certain of the finders in each of said groups being reserved for use as overflow finders, secondary finders having access to the overflow primary finders of a plurality of said groups, means responsive to the origination of a call over one of said lines for initiating the operation of all idle primary finders other than the overflow finders in the group having access to the calling line, and means, effective only'if there are less than a predetermined number of said primary finde s other than the overflow finders idle in said group for initiating the operation of each of said secondary finders which are not in use to select an idle overflow finder in said group.

23. In a telephone system, subscribers lines divided into groups, a group of primary line finders for each group of lines, certain of the finders in each of said groups being reserved for use as overflow finders, secondary finders having access to the overflow primary finders of aplurality of said groups, means responsive to the origination of a call over one of said lines for initiating the operation of all idle primary finders other than the overflow finders in the group having access to the calling line, means effective only if there are less than a predetermined number of'said primary finders other than the overflow finders idle in said groupa'for initiating the operation of each of said secondary finders which are not in use to select an idle overflow finder in said group, and means for causing the operation of each of the idle overflow primary finders in said group in response to seizure by a secondary finder. V GERALD DEAKIN.

nWILLIAM HATTON.

DISC L.A| M E R Y., and William Hutton, Paris, France.

TELEPHONE SYSTEM. Patent dated December 11, 1934. Disclaimer filed November 18, 1937, by the assignee, Western Electric Company, Incorporated.

Hereby enters this disclaimer to claims 4 and 7 of said Letters Patent.

[Ofiie'lal Gazette December 14, 1937.]

1,984,060.Geralcl Deakr'n, New York, N.