US1863716A - Apparatus for the reception and transmission of wave energy in space - Google Patents

Description

June 21, 1932. H. HECHT ET AL APPARATUS FOR THE RECEPTION AND TRANSMISSION OF WAVE ENERGY IN SPACE Filed Nov. 30, 1929 3 Sheets-Shet 1 June 21, 1932. H. HECHT ET AL 1,863,716

APPARATUS FOR THE RECEPTION AND TRANSMISSION OF WAVE ENERGY IN SPACE Filed Nov. 30, 1929 3 Sheets-Sheet 2 HM Hm, WM @W June 21, 1932. H. HECHT ET AL APPARATUS FOR THE RECEPTION AND TRANSMISSION OF WAVE ENERGY IN SPACE 3 Sheets-Sheet 3 w 0 1 m w A /M \u h 0% a I M \\J/ W m \\X i o O Patented June 21, 1932 UNITED STATES PATENT OFFICE HEINRIC H HECHT AND WILHELM RUDOLPH, OF KIEL, GERMANY, ASSIGNORS TO ELECTROACUSTIC GESE'LLSCHAFT MIT BESCHRANKTER HAIETUNG, OF KIEL, GER- MANY, A FIRM F GERMANY APPARATUS FOR THE RECEPTION AND TRANSMISSION OF WAVE ENERGY IN SPACE Application filed November 30, 1929,5eria1 No. 410,763, and in Germany lJecember 6, 1928.

The invention relates to arrangements of a type by which, by means of a plurality of oscillators distributed over a surface, wave energy, for instance, sound, is directionally emitted or received in a plane in which this surface lies. Arrangements dealing with this particular subject matter are disclosed for instance in the U. S. application Serial No. 331,286, filed January 9, 1929, by the present applicant Hecht, and the co-inventor Heinrich Stenzel. Arrangements of this type have. a characteristic which makes possible not only the determination of direction or directional transmission in one plane as described in aforesaid application, but also in space. This applies both to an orderly and an irregular distribution of oscillators, particularly to arrangements in circles, and in simple and combined groups. According to the present invention, such oscillators can be used for directional transmission or reception of wave energy in space by connecting them, in the case of a fixed arrangement in space, with a compensator which allows of swinging the directional vector in s ace.

A most advantageous arrangement 0 this kind is characterized by the feature that it is composed of several individual groups fixed in space to form a complete structure, the different individual groups having their zones of maximum directional and transmitting sharpness respectively in different directions in space, and the swinging of the directional beam or the determination of the direction of the incident energy is carried out by means of so-called compensators. The individual groups may, in this case, be manipulated either by one or more observers separately or at the same time.

Constructional examples of the invention are given in the drawings in which Fig. 1 shows diagrammatically the directive range of a circular group of oscillators,

Fig. 2 an arrangement of oscillators con sisting of three separate circular groups, arranged in three planes at right angles to one another,

Fig. 3 two groups of oscillators consisting of a horizontal circular group and a ver tical linear group,

Fig. 3" shows diagran'nnatically the directive range of a vertical linear group of oscillators,

Fig. 4 shows an oscillator arrangement consisting of three linear groups arranged in space at right angles to one another,

Fig. 5 shows the manner of ascertaining the space bearing with the two linear horizontal groups shown in Fig. 4, 7

Figs. (3 and 6 show plotting devices to taking bearings with an arrangement according to the principle implied in Figs. 4 and 5,

Fig. 6" shows the circuit arrangements of the compensator used in an oscillator arrangement according to Figs. l, 5 and 6, and

Fig. 7 shows another form of plotting device with an oscillator arrangement and principle according to Figs. 4: and 5.

Referring first to Fig. 2, which shows diagrammatically the arrangement for space direction finding, three groups 1, 2, 3 of oscillators (transmitters or receivers) arranged in circles of suitable diameter are provided at the station, which circles have a common center, their circular planes cut-ting one another at right angles. The locations of the oscillators on the circles are represented by small circles. The oscillators are distributed on the circles in equal number and at uniform distances apart. For the transmission or reception of energy in a certain direction, the horizontal characteristic of each circle is used, which yields a main maximum in the plane of this circle To explain first more fully the basis on which the observation with an arrangement such as in Fig. 2 rests, reference is made to the diagrammatic illustration Fig. 1. This diagram shows in perspective view only the azimuth circle with the oscillators distributed over its periphery as indicated by small circles. The plane of this circle is assumed to extend atright angles to the paper. This arrangement by itself is in substance similar to that described in the aforementioned application, Serial No. 331.286. The individual devices while located on a circle, say of ten foot diameter, represent, for instance in case of signal reception from a far distant point, of course only a point denoted in Fig. 1 by P as the center of the circle in whlch the arriving beams center. Let us assume first a signal arriving from a distant point 0, which is located in the plane of the clrcle. The receiving device 6 which the beam 02 emanatlng from 6 passes, receives the sound at a maximum, while the intensity in the adjacent other devices decreases to a degree, the more, the further they are away on the circle from device e Let us now consider only the device e through which beam n is drawn. The signal intensity in this device decreases on eitherside of beam line m, the further the distant origin 0 of the sound is angularly removed to either side of beam in in the plane of circle 1. These signal strengths, if plotted result in a. curve indicated by 71, and the plane of which is located in the plane of circle 1.

If now the distant sound source should move from the point 0 at right angles to the circle plane, namely in the plane of the paper, to the point 0 so that the new sound beam 12 includes an angle of 45 with m. The maximum sound intensity of the signal received by device 6 is then smaller than the maximum received from the same signal source when at 0 This is indicated by theshorter length of beam m. If the source should move from O to either side of beam 72 but at right angles to the paper, an intensity curve similar to f can be plotted as is shown at f The plane of this curve is also at right angles to the paper and passes through n which shows its apex. Thus a number of curves may be plotted bet-ween f and f for sound sources at different angular elevations relatively to the plane of circle 1 which curves are indicated in dotted lines. If this group of curves were surrounded by an envelope, its form might be likened to a flattened fig, which is transversely bisected by the plane of circle 1, and whose stem is theoretically in the center of the circle. For each of the devices such as 6 on the circle, a similar envelope exists. The group of curves shown in Fig. 1 is called the horizontal characteristic of the circular group of devices. With such a horizontal group of devices alone, when arranged in a horizontal circle 1 as shown in Fig. 1, it is still possible to sufficiently exactly determine the azimuth of a sound source, provided the angular elevation of the source above the circle is not beyond 45, at which elevation (see beam 12 the sub-maximum of the characteristic is still about of the main maximum (see beam 724 Similar characteristics may be plotted for the groups of devices arranged in the circles 2 and 3 of Fig. 2.

Now in locating for instance a sound source in space by observing the sound maxima with on the circle throu h the three groups of devices, one would proceed, according to the location of the source the source has the smallest angular elevations.

For instance, as shown in Fig. 2, in case the source is located in the direction a, the groups in circles 2 and 3 would be selected for observation, for direction 6, groups 1 and 3, and for direction 0, groups 1 and 2 would be selected. For the direction a, the devices of group 1 would give no maximum at all, because all devices of this group are symmetrically located to the source in that direction. This is respectively true with regard to direction 0 and group 3, and direction I) and group 2.

g If now the sound source should come from the direction d, which is in front of plane 3, above plane 1, and to the right of plane 2, and if we assume first that the spherical angles a, ,6, y, are equal, observations can be made with any pair of circular groups 12, 1-3, or 2-3 to find the exact direction of beam d. If beam d should shift toward plane 1, observations must certainly be made with group 1, and in addition may be made either with 2 or 3. If beam cl should shift toward plane 2 and toward 3, the best observations can be made with group 2 and 3. If d moves down and more to the front, groups 1 and 2 should be used and so forth.

In general the rule prevails that the best results are obtained alway with thegroups,

whose planes have the smallest angular inclination to the sound beam.

The observer would proceed for instance as follows: He always observes with only one group (in one plane) at a time, and notes the angle in that plane at which the maximum is observed. If he takes for instance group 1 as a basis, he may take the angle found as the azimuth angle, in which case the observations with the two other groups serve for determining the exact elevation of the source. Of these two latter observations the one with the greater maximum would be the more exact observation, because it implies the smaller relative angle. If the two maxima are equal, it is immaterial which of the two elevation values he takes for his calculations.

The described arrangement has the advantage that only a standard circular compensator is necessary which can be used for each of the circular groups of oscillators.

A further simplified arrangement is shown in Fig. 3. It consists of only two groups, namely a horizontal circular group 1 (azimuth circle) and a vertical linear group 4. These groups give together a very useful determination of bearings within a zone of 45 angular elevation above the horizontal plane throughout the whole circle. For the azimuth circle, an explanation has already been given above with reference to Fig. 1.

"i sphere N aroun The linear cup 4 to be used for the determination of l ieight also has its maximum accuracy in a zone which lies within an elevation of about i with respect to a plane at right angles to it. The accuracy of taking bearings in this arrangement, therefore becomes the smaller the nearer the object of which the bearings are to be taken lies to the point vertically above circular group 1. v

In this case the horizontal characteristic of the circular grou 1 is the same as in Fig. l and has been omitted in Fig. 3 for clearness sake. "Only the characteristic of the vertical straight line oscillator group 4 is shown in Fig. 3 for the three elevations a, b, c. The respective individual closed curves are shown in dash lines in perspective i. e. their planes should be assumed to extent at right angles to the paper. They are shown for observation above the horizontal plane and for difi'erent'elevations in one azimuth angle plane only. Thus if the object sought is located in the direction a (left or right) i. e. if the elevation is zero, a symmetrical curve with a very sharp maximum is obtained; at the. elevation b a slightly unsymmetrical curve with a less sharp maximum; and at the elevation 0, far over 45, the unsymmetry and broadness of the maximum are increased to such an extent, that observations at this elevation are of no value for practical purposes.

The observer would in that case proceed as follows: He first ascertains the. azimuth angle, using the circular group 1 according to Fig. 1. Then he uses the vertical row 4 of oscillators to ascertain the elevation. When taking bearings from the ground, the observer is of course only interested in the upper half shown in Fig. 3, because in that case the observation is single valued.

For this arrangement, of course, two different compensators are necessary, one circular compensator for the azimuth circle and one linear compensator.

A particularly advantageous arrangement for taking bearings or for transmission in space is shown in Figs. 4 and 5. It consists of two crossed linear groups of oscillators 5 and 6. The devices are again represented by small circles. Fig. 5 serves for understanding how the determination of bearings is accomplished here. In this figure the two heavy lines 5 and 6 represent the two crossed horizontal linear groups 5 and 6 of Fig. 4. A straight line group is, as is well known, characterized by the feature that the geometric place for all sound sources, which give a maximum at the same adjustment of the compensator, can be considered as the base circle of a cone whose apex is located in the centre M of the linear and whose plane is parallel to the group. This circle can be considered further as bein cut by this cone out of a d M of any assumed radius.

Thus it is clear that, for the base 5, the directions of all sources S of the aforementioned maxima must be located on the cone base circle 8, two generatrix lines of which are indicated by the dash lines Mg and Mh. For the base 6 the directions of all sources S of the aforementioned character would li e on the cone base circle 9 with the two generatrix dash lines Mi and Mk. Part of the base circle 8, shown in full line, is directly visible, the remainder, shown as a dash line, lies behind. The base circle 9, shown in dot-dash lines is entirely on the rear portion ofthe sphere. a

The two points of intersection of these cone base circles indicate .the' exact location of the source in space. lVith the observer in free space, this determination of bearings would be equivocal since the two cone base circles have two points of intersection S and 8,. If. however, the determination of bearings or the transmission is done from the ground, S represents the mirror image of S lying be low the ground and is omitted for the measurement, so that the latter clearly yields the single valued directional ray MS which, geometrically, represents the line of intersection between the two cone surfaces having the bases 8 and 9, and forms the only sound vector, common to both base circles and cone surfaces.

If for direction finding only two crossed linear oscillator groups 5 and 6, Figs. 4 and 5, are used, which are located in a horizontal plane, the direction determination is most exact in the neighborhood of the zenith, and

least exact or broadest in horizontal direction. This disadvantage can be overcome by using a third vertical line of oscillators, such as shown at 7 in Fig. 4, which would be used by the observer as described with reference to Fig. 3.

For measuring purposes with two base lines such as 5 and 6 in Figs. 4 and 5, two linear compensators are used, which, however, are not actuated one after another or by different observers but, better, at the same time by the same observer. They are both connected to the same telephone (or other indicating instrument) in which this observer perceives the indications of the maximum. He has nothing else to do then, by varying the two compensators, to adjust the absolute maximum, for it is clear that the latter, in the example illustrated in Fig. 5. can only occur at the adjustment corresponding to the two cone circles and that a deviation from this adjustment to the one or the other base must necessarily lead to a reduction of the heard or indicated wave energy.

Since both linear groups yield their greatest accuracy when the object whose bearings are to be taken lies near its vertical central plane (median plane), then it is evident that the accuracy of determining bearings here increases toward the apex where it attains its with which, after the above described adjustment, a more accurate redetermination of the height is carried out with the two'compensators of the horizontal group. No spe cial compensation is necessary therefor but,

with the same number and distribution of;

receivers, one of the two compensators of the horizontal groups can "be used for the vertical group.

Concerning working out the measurements, it is clear that, with all those group combinations where the measurement of azimuth and elevation is done by separate measuring operations, the two values on the particular compensators are directly and individually read off on suitable scales. In arrangements of the type where both values are ascertained by a measuring operation and which are explained by aid of Figs. 4 and 5, it appears desirable. also to directly indicate both values at the same time. A fundamental group of possibilities of indicatio ns can be deduced from the consideration of Fig. 5 if it is imagined that a visible guiding element (pointer, light beam or the like) or the two cone base circles are moved on a hemisphere arranged over the bases 5 and 6 and are divided into meridians 5, 6 as polar axes, depending upon the compensators adjustment. Instead, it is also possible to conceive projec tions of the light beam or of the cone base circles moving on the horizontal plane on just such a projection of the hemisphere division. Of course, a division of the hemisphere into longitudinal and latitudinal circles or into greatest sphere circles or a projection of such a division on a plane can also be used.

In Figs. 6 and 6 is illustrated a plotting device for arrangements according to Figs. 4 and 5. On two pairs of rails 120, 121 and 122, 123 only 122 of which is fully drawn, there run two narrow extended frames 124 and 125 across one another. In their particular crossing point there runs in rollers (see also Fig. 6 126 and 127 a carrier 128 for the indicating member. This carrier can be designed as a pointer, as a lamp with projector or in any suitable manner. In Fig. 6 is shown a lamp projecting a sharp light beam, in Fig. 6 a piece of a pointer arm. Above or below the device is arranged a transparent or opaque (depending upon whether a pointer or a light beam is used) plate 129 with the orientation division 130 (indicated by broken lines). It may be carriedout as the projection of a. sphere division into longitudinal and latitudinal circles, or in meridians, or as a hemisphere with original division. The frames are connected through cords 131, 132, 133, 134, with the turning knobs 135 and 136 of the double compensator 137 for the two linear groups and, on turning these knobs, the frames are positively moved. It is immediately clear that the two frames must be connected with the contact device of the artificial line compensator in such a way, or the latter must be so arranged, that the crossing point of the frames keeps the particula P011113 0f p j tion of the point of intersection of the two cone base circles on the horizontal plane of Fig. 5. In case of a hemispherical transparent or translucent orientation chart, the point at. which the light strikes the chart corresponds to the exact location of the space vector, which is the point of intersection of the aforementioned cone base circles, or, in case of a plane orientation chart, as shown in Fig. 6, to its point of projection.

Fig. 6 shows, in the simplest form, the circuit of an installation'according to Figs. 4, 5 and 6, and substantially on the principle disclosed in the aforementioned application. For each linear group of devices, only three receivers 161, 162, 163 and 164, 165, 166 respectively are assumed. The centre receiver can be common for both groups but is illustrated here as a double receiver, (one in full, the other in dotted line) in order not to complicate the clearness of the illustration. Each group of receivers is connected with a changeover switch 167 and 168 which allows of changing-over the receiver connections with the compensator. This changing over has the purpose of completely utilizing the compensator for the angles 0 to 90 and 90 to 180, that is, to manage with half the length of the artificial lines in the compensator. It is desirable, however, to dimension the com pensator somewhat greater in order that it need not be reversed just at the apex. The outermost receiver of each group (in the illustrated example 163 and 166) is directly connected, and every other one is connected through its contact slide in the compensator to the primary coil of its respective transformer 171, 172, 173 or 174, 175, 176. The secondary coils of these transformers are all connected in series and through the amplifier 169 to thetelephone 170. The chain of the compensator is divided into equal steps and connected to the circular rows of contacts 177, 178 or 179, 180 of the compensators in such a way that between successive contacts, in the sequence of the receivers in the linear receiver groups 5 and 6, Fig. 4, the second receiver in each case is switched forward by the amount of one chain section of the compensator line and the third receiver in each case by the amount of two sections, and so on. With each contact row isassociated a circular contact rail 181, 182 and 183, 184 respectively which is connected with the corresponding transformer. The connection between each contact row and its rail is effected by brushes 185, 186 and 187, 188 respectively, which are carried by a rotatable contact arm. Connected to the contact arm is the element coupling which serves for actuating the indicating mechanism, aforedescribed with reference to Fig. 6, andwhich is represented in the constructional example by the cords 189, 190.

If an artificial line of the double compensator of Fig. 6 is to be used separately for a vertical linear group, such as 7 in Fig. 4, for more accurate re-determination of the elevation, this can be accomplished by means of the two switches 191 and 192, the first of which effects the reversal to the vertical linear group of receivers, of which at switch 191 only short leads from the contact points are shown whilst the second 192 disconnects the transformers of the right hand side and changes the connection to the amplifier. The reading of the height is then done on a particular height scale 193.

In Fig. 7 an arrangement, in principle similar to Fig. 6, is diagrammatically illustrated. Instead of the linear frames 124, 125 of Fig. 6 spherical shell portions or frames 140, 141 are used, one within the other and. provided with peripheral slits 142, 143 respectively,

- electric waves.

which cross each other at right angles. The frames are pivoted respectively on crossed axles 144, 145. Axle 144 lies within the inner spherical shell or frame, while axle 145, mounted in the frame 146, consists of two alined but separated parts, in order to accommodate the inner shell 140. In the common center of the spherical shells or frames is mounted a ball and socket joint 147, carrying an arm 148, which similarly as described with reference to Fi 6, runs in rollers at the points where it passes through slits 142 and 143. It may be designed as a pointer or a carrier of a lamp with a point beam projector. In the present case it is assumed to carry a lamp throwing a point beam.

For orientation purposes is used a transparent or a translucent spherical envelope divided into longitudinal and latitudinal degrces, or it may be divided into meridians or into greatest sphere circles. The movement of the beam is effected again by the contact operating device of the compensator lines, for instance. by cords 150, 151 through the turning knobs 153, 152 respectively of the compensator 154.

Arrangements of the described type can be employed equally advantageously for the transmission and reception of wave energy of any kind, for instance, sound waves and In the latter case, the mechanical oscillators are to be replaced by electrical oscillators, preferably by those characteristic. Arrangements of the described type with sound receivers serve, with particular advantage on flying fields for loeating aircraft.

The illustrated general forms are, of course, only examples of the manner in which our invention may be reduced to practice, and should not imply a limitation of the group combinations or the construction of the compensation or the indicating devices. With respect to the grouping of the receivers the main feature is that always a plurality of groups is used, whose individual characteristics as geometrical loci for difi'erent planes are so combined, that one single valued resulting geometrical locus for the sought object obtained. The indicating devices, of course, can also be designed to make records instead of giving momentary visible indicacations as shown. The construction of the transmitters or receivers is not of importance in carrying out the idea of the invention, so long as care is taken that these apparatus work as true as possible with respect to phase and amplitude, that is, without distortion.

We claim 1. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprising at least two groups of oscillators arranged with their eifective directive ranges in different planes crossing each other, an independent compensation means for each group adapted to vary the directional character of its group within its range, to obtain maximum wave energy effects-in the desired direction, and means for combining the resultant maximum directional effects of the two groups to obtain a definite single valued maximum directive wave energy effect in space.

2. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprising at least two similar groups of oscillators arranged with their effective directive ranges in different planes crossing each other at right angles, an independent compensation means for each group adapted to vary the directional character of its group within its range, to obtain maximum wave energy effects in the desired direction, and means for combining the resultant maximum directional effects of the two groups to obtain a definite single valued maximum directive wave energy effect in space.

3. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprising in com bination two similar linear groups of oscillators positioned in one plane and crossing one an other at right angles, an independent compensator for each group, adapted to vary the which themselves have no natural directionaldirectional character of its group within the directive range of the group to obtain maximum wave energy effects in the desired directions, and means for combining thcresultant 5 maximum directional effects of the two groups to obtain a definite single valued maximum directive wave energy effect in space.

4. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprising in combination two similar linear groups of oscillators positioned in one plane and crossing one another at right angles, and a third similar linear oscillator group arranged in the crossing point of and at right angles to the two first named groups, an independent compensator for each group adapted to vary the directional character of its group within the directive range of the group to obtain maximum wave energy effects in the desired directions, and means for combining the resultant maximum directional effects of two groups to obtain a definite single valued maximum directive wave energy effect in space.

5. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprising in combination two similar linear groups of oscillators positioned in one plane and crossing one another at right angles, and a third similar linear oscillator group, arranged in the crossing point of, and at right angles to the two first named groups, an electrical compensator for each of two groups, comprising an artificial line adapted to vary the directional effect of its group within the directional range of the group to obtain maximum wave energy effects in the desired directions, a switching device for switching one of said of oscillators, and means for combining the resultant maximum directional effects of the chosen two of said three groups to obtain a definite single valued maximum wave energy effect in space.

6. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprising at least two groups of oscillators arranged with their effective directive ranges in different planes crossing each other, an independent compensation means for each group, comprising an artificial line, adapted to vary the directional character of its group within its range, to obtain maximum wave energy effects in the desired directions. and an indicator connected to all of said artificial lines for indicating the combined directional efiects of the two groups to obtain a definite single valued directive indication in space.

7. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprising at least two groups of oscillators arranged with their efiective directive ranges in different planes compensators over to the third linear group" crossing each other, an independent compen-' dicating device on which chart the space direction of said single valued maximum effect is indicated by said vlsual indicator.

8. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprising at least two groups of oscillators arranged with their effective directive ranges in different planes crossing each other, an independent compensation means for each group, comprising an artificial line and an adjusting device for varying said line, to vary the directional character of the pertaining oscillator group within its range to obtain a maximum wave energy effect in the desired directions, an indicator connected simultaneously to all of said artificial lines for indicating the combined directional effects as a single valued maximum, a guiding device for each of said adjusting devices mechanically coupled to it, a visual indicating device having means for projecting a point light beam, and being guided by both of said guiding devices, and a transparent orientation chart located within the operating range of said light beam and on which the latter indicates the space direction of said single valued maximum effect.

9. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprising at least two groups of oscillators arranged with their effective directive ranges in different planes crossing each other, an independent compensation means for each group, comprising an artificial line and an adjusting device for varying said line, to vary the directional character of the pertaining oscillator group within its range to obtain a maximum wave energy effect in the desired directions, an indicator connected simultaneously to all of said artificial lines for indicating the combined directional effects as a single valued maximum, a guiding device for each of said adjusting devices mechanically coupled to it, a visual indicating device having means for projecting a, point light beam, and being guided by both of said guidingdevices, and a hemispherical transparent orientation chart located within the operating range of said light beam and on which the latter indicates the space direction of said single valued maximum effect.

10. Arrangement for directional transmission and reception of wave energy in any desired direction in space, comprlsing at least two groups of oscillators arranged with their effective directive ranges in different planes crossing each other, an independent compensation means for each group, comprising an artificial line and an adjusting device for varying said line, to vary the directional character of the pertaining oscillator group within its range to obtain a maximum wave energy effect in the desired directions, mindicator connected simultaneously to all of said artificial lines for indicating the combined directional effects as a single valued maximum, an elongated guide frame for and coupled to each of said adjusting devices, and

go movable by its pertaining adjusting device transversely to its axis, said two frames being arranged at right angles to one another, a visual indicating device guided by both guide frames, and an orientation chart cooperatively associated with said visual indicating device on which chart the space direction of said single valued maximum eflfect is indicated by said visual indicator.

In testimony whereof we alfix our signa- 30 tures.

HEINRICH HEGHT. WILHELM RUDOLPH.

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