US1613686A - Method of and apparatus for secret electrical transmission of pictures - Google Patents

Description

on u 000.0.. ooooo 1927.. Mn M G. s. VERNAM METHOD 0F AD APPARATUS FOR SECRET ELECTRICAL TRANSMISSION OF PICTURES Filed Deo. 5, 1924 2 Sheets-Sheet l www oooooo oooo INVENTOR W/fmm/ ATTORNEY Jan.. TIL M927. A

G. S. VERNAM METHOD OF AND APPARATUS FOR SECRET ELECTRICAL TRANSMISSION CF PICTURES Filed Dec. 5, 1924 2 Sheets-Sheet 2' IVI?,

' INVENTOR f i 51 iwf/@mw BY ATTORNEY Patented Jan'. 1l, 1927.

UNITED `STATES PATENT' OFFICE.

GILBERT S. VERNAM, OF'RIVEB EDGE, NEW JERSEY, ASSIGNOB TO AMERICAN TELE- PHONE AND TELEGBAPH COMPANY, A CORPORATION OF NEW YORK.

METHOD OF AND APPARATUBFOR SECRET ELECTRICAL TRANSMISSION OF PICTURES.

This invention relates to an improved method of and apparatus 'for transmitting pictures to a distance/by electrical impulses. One of the objects of the invention is to provide for analyzing a picture into small elements of area and transmitting code combinations corresponding to the degree of shade of the successive elements. Another object of the invention has relation to transmitting a single code combination for va sequence lof elements of like shade, the combination indicatin both the degree of shade and the number o elements in sequence. A further object of the invention consists in providingA for absolute secrecy in the transmission of the code combinations sent out v4representing the elements of the icture so that any unauthorized person W o might have acce to the medium through or over which these code combinations might be transmitted would not be able to obtain alikeness of the picture therefrom. These and various other objects and advantages of the invention will become apparent on consideration of the specific example of the practice of the invention which we have chosen to disclose in the following specification and illustrate in vthe accompanying drawings. It will be understood that the invention is defined in the appended claims and that the following specification relates to the particular example here presented to illustrate the invention.

Referring to the drawings, Figure 1 is a circuit diagram showing the transmitting y apparatus, Fig. 2 is a plan showing the code as punched in a section of the tape, and Fig. 3 is a circuit diagram showing the receiving apparatus.

The picture to be transmitted is in the form of' a semi-transparent film 75 which is wrapped about the glass drum 76; this drum is rotated on its' axis and meanwhile traversed relatively slowly along its axis so that the portion of the film 75 adjacent t0 the opening in the screen 74 describes a helical course of adjacent turns on the film 75.v

The light from source 73 shining through the opening in the screen 74 and through the underlying portion of the film 75 falls on the photoelectric cell 77. rThe current in the circuit of the cell 77 is accordingly varied in correspondence with the varying degree of shade in the spot of the film 75 adjacent to the opening in the Screen 74;. rlhifs vary- Application led December 5, 1924. i Serial No. 754,166.

ing current through the cell 77' causes a correspondingly varyin electromotive force in the input circuit o? the amplifier 78 and amplifier 79. Three marginal polar selecting relays A, B and C are inthe output circuit of amplifier 79. The adjustments of these relays are such that for a part of the film 75.corresponding to White none of the relays A, B or C will operate; for light gray only A will be operated; for dark gray A and B will operate but not C; and for black all three relays A, B and C will be operated. l

The cams 18 and 19 rotate once for each unit or element of the picture film 75 lying under the opening of the screen 74.

The tape shown in Fig. 2 is punched with a code ,combination when the shade changes to indicate the preceding shade and to in-Y dicate the number of picture elements in sequence having that same shade. The code employed is the usual five unit code, the same as for ordinary printing telegraphy. The third and fifth positions are for the four degrees of shade, and the first, second and fourth positions are for the number of unit elements in the sequence having the same shade. As shown in Fig. 2, this number of units permits counting a number of elements up to seven inclusive, and as will be pointed out presently, if a sequence of seven elements of like shade is encountered in the picture to be transmitted the count is made to seven and then the apparatus is cleared ready to repeat.

Suppose that a single white unit inthe picture film 75 is to be transmitted. A glance at Fig. 2 shows that the corresponding code impression in the tape comprises holes punched in the first and third positions, the punch in the first position meaning a single unit and the punch in the third pos1- tion meaning the white shade.

As already stated, for the white shade the current in the output circuit of the amplifier 79 will be so low that none of the marginal relays A, B and C will be operated, and their armatures willall be on their lower or spacing contacts.'

With the armature of relay A on its spacing contact, relay a will be energized so that when the cam 19 closes contact 25 a circuit will be made through the back contact of relay c, front Contact of relay a, back Contact of relay a', to the perforator relay 20, which dll@ till

till

will cause the later to lock up and energize the punch magnet 21. This will punch 1n the tape whatever combination is set up atl the time by the selecting magnets 1, 2, 3, 4 'and 5 and this combination will show the )receding shade in the picture and the numer of picture elements having that shade.

The operation of the punch magnet 21 closes a circuit from the positive battery 23, through the upper Winding of relay a and causes it to operate. Also the operation of the punch magnet 2l breaks the locking circuits for the relays b', and e', and releases them if they or either of them have previously been locked up. Also the operation of the punch magnet 21 releases any of the counting relays 1a, 1b, 2, etc., that may have been locked up previously. The operation' of the punch magnet 2l also breaks the locking circuit for the perforator relay 20, wh ich opens and thereby releases the punch magnet. The release of the punch magnet then closes a circuit from the battery 23, through the lower back contact of relay c', and the lower front contact and Winding of relay a to lock up relay a. Also, the operation of relay 'an' closes the circuit to energize the selector magnet 3.

The cam 19 continues to rotate and closes a contact at 24, the counting contact. This closes a circuit from battery through the upper back contact of relay c', back contact of relay 1b and the Winding or relay 1, which latter relay operates accordingly. This connects battery 23 through the back contact of relay 4b and the front contact and armature of 1 to the winding of 1b, but lb does not operate at this time because it is already shunted by the low resistance path just traced, through the contacts at 24, c and 1".

.Also, the operation ot relay 1a closes the circuit for selecting magnet 1 and causes it to to operate. It is pointed out at this point that the circuits of the selecting magnets 1, 27 3, 4 and 5 are'notconnected directly to negative battery but are connected to the negative bus-bar of a key tape transmitter 71 provided for purposes of secrecyv as will be pointed out in detail hereinafter. To set up the combinations in unciphered form, as shown in the code of Fig. 2, a blank tape will be inserted in transmitter 71 .to hold the contacts on the negative bus-bar.

When the counting contact 24 opens, this opens the shunt around relay 1b, which operates and transfers the counting circuits (through the upper back contact of relay 0') so that now, instead of connecting to 1 and 1b, it connects to 2a and 2b.

`We have already assumed that only a single element of White shade is to be transmitted so that acordingly the shade will now change. Assume that it changes to light gray. Marginal relay A` Will be energized and relay a Will be released. When the cam `operates as prev1ously described and the punch magnet 21 operates as described before, and selector magnets 1 and 3 having been previously energized, holes are punched at the first and third positions, as shown in Fig. 2. The operation of the punch magnet 21 releases the counting relays and relay a by breaking their circuit at the contact adjacent to battery 23, and the system is ready to start over again. The perforator selecting magnets will also be released at this time.

Let lus go back and suppose that instead of a single White element in the lihn 75 there were five such elements in succession. Then, When the punch Contact closes, instead oll Getting the result last described, the perforator relay 20 will not operate because its circuit Will be open at the back contacts of relays a and a. However, the counting contact 24 Will close a circuit from battery, through the upper back contact of relay 0', iront contact oi relay l", back contact ot relay 2b, through the Winding ot counting relay 2, which will operate at once. By the operation of 2, battery 23 will be applied to the Winding of relay 2", and as soon as the Contact 24 opens, opening the shunt around 2b, battery 23 will become edective and operate 2b as Well as 21. Perforator selecting magnet 2 will be energized at this time.

0n the neat revolution of theV cams 18 and 19 corresponding to the next element of the picture `iilm 75, counting relays 3a and 3l will be operated and locked up in similar manner. Selecting magnet 1 Will be released. Then, on the next rotation ot the cams 18 and 19 for another element of the film 75, relays 4a and 4b will be operated in like manner. lt will be noticed that relay 4d has its winding in series with a Winding of relay 4c so that relay 4c operates simultaneously with 4a and 4c locks up by current from the battery 23 through its lower winding. Also 4c closes a direct circuit i'rom battery, through the selecting magnet 4. which operates at this time.

When the counting contact at 24 opens after the fourth count, relay 4b operates by reason of the opening of the shunt around it. The operation of 4b breaks the circuit from battery 23 to the relays la, 1, 2, 2h, 3a and 3", and allows them to release, releasing also selecting magnet 2. Then, when 2b releases it breaks at its upper front contact the circuit for 4a and 4b but relay 4c remains locked up.

0n the fifth revolution of the cams 13 and 19 corresponding to the lifth successive element of White shade in the film 75, the

lOl)

Leiaeea relays 1a and 1b are operated again successively upon the closure and subsequent opening of the contact 24, causing selecting magnet 1 to be operated. After the fifth revolution the shade changes in the film` 75, operating one or more` of the relays A, B and C and thus, as described heretofore,

' establishing a circuit for the perforator relay 20 and allowing the punch magnet 21 to operate and punch holes at positions 1, 3 and 4, indicating a sequence of tive `white elements, as shown in Fig. 2. The operation of the punch magnet 21 clears the counting relays by breaking the circuit from battery 23, as previously described.

1f a shade recurs more than seven times in succession a punch will be made on the seventh count and the count will be begun again for another series. We have already seen that on the fourth count the relay 4c locks u on the fifth count 1a and 1b are operate( on the sixth count relays 2a and 2b are operated, and on the seventh count relays 3a and 3h are operated. 3b closes at its upper front contact a circuit to battery, through the winding of perforator relay 20, upper front contact of relay 4c, back contact of relay 4n and upper front contact of relay 3", when this circuit is completed at 25 to loperate the perforator relay 20 and the punch magnet 21. The operation of the punch magnet 21 punches holes in the second and fourth positions to indicate seven elements of like shade, and other holes (or a blank) in other positions to indicate'the degree of shade. Also, the operation ofthe punch magnet 21 clears out the counting relays, as described heretofore, ready to begin over again.

A margin contact 80 is associated with the transmitting drum 76 and is closed through to a battery at the edge of the film 75. The circuit thus established through the winding of relay 0 energizes the latter and closes the upper front contact of relay c so that when the punching contact is made at 25 the circuit is closed for the -perforator relay 20, thereby causing the punch magnet 21 to punch whatever combination happens to be set up at that time, that is, when the edge of the film is reached by the contact 80. 'llie operation of the punch magnet 21 clears out the counting relays, as has been described, and causes the relay o to be picked up and locked up by current from the battery 23. This condition' continues until the other edge of the film 75 reaches the contact .the contact is broken, relay c releases and the circuit for perforator relay 20 is established through the upper back contacts of relay c and a frontcontact of relay o', which remains locked u The circuits ot" relays a and b are bot o en at the lower back contact of relay cv at t is time and the counting relays are all released and therefore all the selecting magnets will be deenergized so that when the contact- 25 is closed and the perforator relay 20 operates, causing the punch magnet 21 to operate, the blankcombination will occur on the tape, which is the code for `carriage return and line feed. This will be explained further in connection 'with the discussion of the receiving apparatus that is to follow.

Aocontactperatedby the cam 18 closes briefly for each element of the picture,`shunt ing out the marginal relays A, B and'C. Thisallows them to operate always onvthe same point on their magnetization curves for the same shade, that is, on an increasing and not a decreasing current. The contact at 18 is closed momentarily, immediately after the punch contact at 25 opens, and this gives the marginal relays A, B and C sulicient time to release and o erate again before the next punching com ination.

In order to provide for secrecy 'in the transmission of the code combinations set up on the perforator selecting magnets 1, 2, 3, 4 and 5, a tape transmitter 71 is provided, having positive and negative bus-bars and a tape feed magnet 72, controlled byl the perforator relay 20. If ,a blank key tape were inserted in this key tape transmitter 71 so that all of the contacts would be` against the negative bus-bar, as pointed out previously, the code combinations set up on the selecting magnets 1, 2, 3, 4 and 5 would correspond to the code illustrated in the tape of Fig. 2. However, a cipher key tape having 'a series of arbitrarily chosen code combinations will be inserted in the tape transmitter 71 and these code combinations will be combined, in effect, with the code combinations which would-otherwise be set up on the selecting magnets 1, 2, 3, 4 and 5, in order to produce a scrambled or unintelligible set of code combinations for transmission to the distant station. Such a cipher system is disclosed in detail in United States Patent No. 1.310,719, in the name of G. S. Vernam, and for a more complete understanding of' the principles of operation thereof reference may be had to this patent.

@ne end of the winding of each of the perforator selecting magnets 1, 2, 3, 4 and 5 is shownconnected to a corresponding contact of the tape transmitter 71. If the contacts of this tape transmitter are all resting against the lower bus-bar, `as shown in the drawing, so as to connect the selecting magnets to the negative side of the power supply, the operation ofthe perforator and the relays would give a normal indication of the v HMI) llo

inserted in the tape transmitter 71 and any of the transmitter contacts are thereby allowed to move against the upper or positive bus-bar, the action of the relay contacts on the corresponding selecting magnets will be reversed. For example, we may assume that the code combination representing two light gray picture elements is to be recorded in order to print two small dots or periods at the receiving station. In this case the selecting relays will all be released and the counting rela s 1, 1", 2, and 2b will be energized. s wouldV normally ener ize perforator selecting magnets 1 and 2. I we assume that the contacts 1,3 and 4 of the tapetransmitter 71 are against the upper bus-bar, the return side of the windings of selecting magnets 1, 3 and 4 will be connected to the positive terminal of the power supply, while magnets 2 and 5 will remain connected to the negative terminal. As relay 1 is energized and relay 3 deenergized, both ends of the Winding of selecting magnet 1 will be connected to positive polarity, and this magnet will not beA energized. Magnet 2 will be connected to the positive terminal at the front contact of relay 2, and to the negative terminal at the lower bus-bar of the tape transmitter. 4Thismagnet will, therefore, be energized. Magnets 3 and 4 will be connected to positive at the transmitter and to negative at the back contacts of relays a and 4?, respectivel. These magnets will both be ener ze Magnet 5 will have negative potentie. 'applied to both endsof its windings and will remain deenergized. When the punch magnet operates, the combination 2, 3, 4 will be perforated therefore, instead of the normal combination l, 2. This form of code combination iiormally re resents seven white elements or spaces so at the key tape has, in edect, ciphered the code combination in the perforator tape so as to change the number of repetitions as well as the shade it represents. When the perforator relay 20 operates to energize the punch magnet 21 it also establishes a circuit for operating the tape feed magnet 7,2 of the tape transmitter a key tape identical with the one utilized at the sending station to scramble the picture message. This key tape will be inariane serted in the key ta e transmitter 34. vThe code combination o the key tape will then combine in effect with the code combination of the enciphered. icture message tape to set up on the selectin relays 11, 22, '33, 44, and 55 the code com inations representing the elements of the picture just as if these had not been sent out in encipherd form from the sending station. The principles of this operation are explained in detail in the aforementioned Patent 1,310,719.1'10 G. S. Vernam. For purposes of illustration let it be assumed that the scrambled code combination, heretofore referred to sent out representing two light gray elements is to be iinscrainble cording to the code illustrated in Fig. 2 would be 1, 2. When this was sent out in scrambled form it resulted in 2, 3, 4. Accordingly, the combinations 2, 3, 4 will be set up in the messa e transmitter 34 and the ode combination in the key tape in the transmitter 34 will be 1, 3, 4. Under these conditions the selecting relays 11 and 22 will be energized as the terminals `of their windings are connected to oppositely poled bus-bars, while the relays 33, 44 and 55 will remain deenergized. The combination set up in the selecting relays will accordingly be 1, 2 which according to the code represents two light gray elements. Accordingly, the printer at thev receiving station will record two small dots or periods in a manner to be pointed out in more detail hereinafter.

The printing is done on a pa e as in a page printing receiver in whic t e printer selecting ma ets 110, 220, 330, 440 and 550 are employe Magnet 110 is unnecessary for picture printing and the remaining four magnets mentioned operate according to the following code:

Printer select- Characters printed ing magnets and other printer operated operations 330 Space or blank. None. Small dot.

550 Medium dot. 330, 440, 550 Large dot.

440 Carriage return. 221) Line feed.

This particular code arrangement is shown as one suited for use in connection with certain ordinary 'printing telegraph machines now widely used.

The enciphercd picture message ta'pe, as'

This code combination ac aeiaeae relays with which they are connected before the contact S closes at 38.

Tf relay 33 of the two shade selectin relays is energized, then when contact closes, battery 36 will be connected through printer selecting magnet- 330. rIhis will cause the printer to record a space orl blank as indicated in the foregoing table. lif relay 55, but not 33, is energized, the contact closure at S will connect the battery to printer selecting magnet 550 and a medium'dot will be printed. If relays 33 and 55 are both energized, then contact closure at S will apply battery to magnets,

330, 440 and 550 in parallel and a large'dot will be printed. Tf neither relay 33 nor 55 is energized, no impulse will be sent through the printer selecting magnets, and a small dotwill be printed.

For example, to explain the faction of the counting relays 11, 22 and 44, let it be assumed that the code combination 1, 2, 5 has been set up on the selecting relays 1. A reference to Fig. 2 shows that this corresponds to a sequence of two medium dots. The relays 11, 22 and 55 are accordingly in energized condition. When the cam 38 closes contact S, printer selecting magnet 550 will be energized thus preparing the printer for recording a medium dot. At the same time the relay 11x71 will be energized by the closure of a circuit from batter 36, through contact S, and through 'the ack contact of relay 11b. Accordingly, the relay 11a will connect battery 39 to the lower end of the winding of relay 11h, but relay 11b will not operate until contact S opens, because meanwhile relay 11b is shunted through said contact S. When relay 11b does operate, it transfers' the counting circuit 37 to the armature of relay 22b and thence to the winding of relay 22a.

As the cam 38 continues to rotate, contact T will be closed and connect battery through the front contacts of relays 11, 11a to the armatures of the relays 22,. 22a and 33a but as these are all opened, the transmitter magnets 32 and 32 will not be energized. When contact S closes on `the next revolution, the printer selecting magnet 550 will be energized again to cause the printer to record another medium dot, and

relays 22aL and 22b will be energized in succession in the manner heretofore described for 11a and 11b. Then when contact T is again closed by the further rotation of the 1 H MIN cam 38, battery will he connected through T andthe front contacts of rela s 11, 11am and 22B and the back contact o relay 44 to the windings of the clear-out'relay 31 and tape transmitter magnets 32 and 32. The tapes will now step ahead to new signal combinations. The actuation ofthe clear-out relay 31 establishes a direct circuit from battery through the contact T and front contact of relay 31, through said relay 31 and the tape transmitter magnets 32 and 32'; this insures that the tape transmitters 34 and 34 will receive a full length impulse. The opening of the back contact of relay 31 removes battery 39 from the countin relays and releases them.

lin w at goes before, we have traced the operation for the code combination 1, 2 and 5 corresponding to a sequence of two medium dots as shown in Fig. 2. 1 and 2 determine the count and 5 determinesthe shade. Assuming that the shade i's the same, other settings of the count selecting rela s 11, 22 and 44 will cause the selected sha e character to be recorded a different number of times as follows:

If relay 11 is energized alone, the tape feed circuit controlled at T will be closed through the front contacts of relays 11 and 11a and back contacts of relays 22 and 44 after a single contact closure at S. If relays 11 and 22 are both operated, the said tape feed circuit controlled at T will remain open until contact S has operated twice as in the case previously followed through in detail. If relay 22 alone is operated, contact S must operate three times so as to energize relays 11g-22a and 33El and then close the tape feed circuit controlled at T through the back contact of rela 11, front contacts of relays 33a and 22 an back contact of relay 44.

If relay 44 alone is operated, four revolutions of the cam 38 must take place which .will operate all four of the pairs of counting relays. Thereupon, with the operation of the relay 44, the repeat relay 41 will operate and lock by current from battery 39. Relay 44b releases all the counting relays to the left thereof, and relay 33b then releases 44a and 44b so that after four operations of contact S `the repeat relay 41 is the only relay remaining energized of the counting group. The tape feed circuit controlled by T is now closed through back contacts of relays 11, 11a' and 22 and theV characters, are the same respectively, as for counts of 1, 2 or 3 as described heretofore, except that in each 'case the tape feed oircuit extends through the front contact of the relay 41 instead of the back contact of rela 44.

The foregoing description covers the o erations of printing from one to seven ike characters from the res ctive code combinations of the tape. e carriage return and line feed operations will now be described. In this case when the contact T opens, all five selecting relays 11, 22, 33, 44 and will remain deenergized. Then when contact S closes, a circuit will be established from battery, through back contacts of relays 44, 22, 11 and 22b to printer selecting magnet 440, which, in accordance with thc foregoing table controls the carriage return operation of the printer. Relays 11 and 11b will also be operated by the closure and subsequent openmg of contact S, and on the second revolution of the cam 38 a second impulse will be sent through magnet/440 over the same circuit as before. This will have no eiect on the printer except to provide more time for the carriage to return, and at this time relays 225l and 22h will be ener `ze d. Then when contact S closes the thir time,an impulse will be sent through printer selecting magnet 220, instead of 440 (due to the energization of relay 22h). This causes the printer to feed the paper one linel in accordance with the last entry in the foregoing table, and at the same time relays 33EL and 33h are energized. When contact T closes, the tape transmitter magnet 32 will be energized over a circuit from T, through back contact of relay l1, front contacts of 33a and`22a, back contact of relay 44, winding of relay .31 and tape transmitter magnet 32 to battery.

Thus it will be seen that, with the deciphered code combinations reproduced at the receiving stat-ion in accordance with the code of Fig. 2, the code combinations control the receiving printer to print a space or a dot of varying size and to repeat each such Yspace or dot any number of times from one up to seven, and automatically to perform the operations of`carriage return and line feed.

While the arrangements of the invention have been disclosed in certain specific arrangements which are deemed desirable. it is understood that they are capable of embodiment in many and Widely varied forms without departing from the spirit of the invention as defined by the appended claims.

What is claimed is:

1. The method of secretly transmitting a picture which consists in analyzing it into sequences of elements of like shade, setting up code combinations re resenting the number of elements in eac sequence and the imacat shade of those elements, combining these code combinations in effect with a series of arbitraril chosen code lcombinations, and transmitting the code combinations resulting from such combinin 2. The method cig secretly transmitting a picture which consists in analyzing it into sequences of elements of like shade, setting up code combinations re resenting the num-- ber vof elements in eac sequence'and the shade of those elements, changing the character of these code combinations in an arbitrary and varied manner, and trans,

mitting said code combinations changed. I

3. The method ofrsecretly transmitting a picture which consists in'analyzing it into sequences of elements of like shade, setting up code combinations representing the number of elements in each sequence and the shade of those elements, combining these code combinations in effect with a series of arbitraril chosen code combinations, transmitting t e resulting code combinations to a distant station, recombining said resulting code combinations at said distant station with a series of arbitrarily chosen code combinations similar to the series utilized at said first station to restore said resulting code combinations to the original state, and

reproducin the picture from said restored code combinations.

4. In a picture transmitting system, means to explore successive elements of the picture and to set up code combinations corresponding both to the number of elements in a seuence of like shade and to the shade of t e elements of such sequence, and means for combining in effect said code combinations with a series of arbitrarily chosen code combinations.

5. 1n a picture transmitting system, a lurality of selecting ma nets, means wherey successive elements ofg the picture may be explored, means whereby there may be set up on said magnets code combinations corresponding both to the number of elements in a sequence of like shade and to the shade of the elements of such sequence, a key tape transmitter associated with said magnets, and a key tape therefor having a ser1es of arbitrarily chosen code combinations thereon Where y the operation of said magnets Will be under the joint control of said key vtape combinations and said rst mentioned combinations.

6. The method of secretly transmitting a picture which consists in analyzing it into elements of dierent shades, setting up code combinations representing said elements of di'erent shades, combining these code combinations in e'ect with a series of arbitrarily chosen code combinations, and transmitting the code combinations resulting from such combining.

lll

renace@ binations with a series of arbitrarily chosen code combinations, and means for reproducing the picture from said combined code combinations.

8. rlhe method of transmitting a picture which consists in exploring the elements thereof successivel for degree of shade, counting the num er of elements of like shades in a sequence,makin0 a non-pictorial record of the number and shade of the counted elements in each sequence, combining the e'ects of said non-pictorial records with another arbitrarily chosen non-pictorial record, transmitting currents controlled by said combined non-pictorial records, and i printing the picture from the received currents.-

In testimony whereof, l have signed my name to this specification this 4th day of December, 1924.

' GILBERT S. VERNAM.

lid

Images