REF ID:A10515. 

Be it known that we, William F. Friedman, and Joseph O.Mauborgne, both residents ot Washington, in the District ot Columbia, have 

invented new and useful improvements in signaling systems, of' which the 

following, taken in connection with the accompanying drawings, is a f'ull, 

clear, and exact description. 

This invention relates to the transmission of' signaling or other 

waves, and deals particularly with the obtaining of secrecy in such transmission. 

It is an object of' this invention to transmit with secrecy 

signals or other waves used in the transmission of' intelligence by any 

of the now well-known methods of transmitting photographs by eiectrical 

means. 

. In what follows, it will be convenient to refer to the material 

that constitutes the elements or data of' the transmission in terms corresponding to those employed in cryptography. Thus, in cryptography the 

original or intelligible matter to be communicated to t.he correspondent 

is called the clear text; the final, unintelligible, or secret matter 

transmitted to the correspondent is called the cryptographic text, or 

cipher text, or often simply, the cryptograph; and in certain cases where 

-l-

@'pp roved for Release by NSA on 09-11-2013 pursuantto E .0. 1352a 
REF ID:A1051~ 

the method ot enciphering involves the use of an independent text the 

letters.or which are employed as successive key letters in the encipher• 

ing or deciphering process. and are known only to the correspondents. this 

intermediate text is referred to as the key text. Since this invention 

deals with secrecy in the art or space or wire radi~the original or intelligible photograph to be communicated to the correspondent 

will be called the "clear photograph"• the adjective 11 clear11 , or course. 

here having no reference to the quality or the photograph, but simply in-

~ 

dicating that it corresponds~ its meaning:t:.the equivalent phrase in 

cryptography, ''clear text". 'rhe clear photograph may be a 8 posit.ive11 or 

a "negative"• oelluloi~.transparency; °"'~-~ •• .W.n pape•-41cn8'pa:i:eru•)llS it may ,.... 

be a photograph at any description whatsoever - a house, a person, a scene, 

and so on. It may be• for purposes ot this description. a photograph ot 

a hand-drawn eketch,·a drawing, a map. and so on; it may be a sheet ot 

. . ~~.(A..~~. translucent paper upon which words have been typewritten or printe'?\. In 

short. any material that can now be transmitted by space or wire rllidio-

~alls within the class ot things for which our invention pro- , 

vides a method and means or transmitting with secrecy. 

Equivalent to the term cryptograph as employed in cryptography. 

the term cryptophotograph will here be used in referring to the enciphered 

or secret torm or the clear photograph. The cryptophotograph is 8 un1n-

-2-
• REF ID:A10515f 

' 

lhll. ·~ ~ • . 

telligible 0 in the sense that it 001!1:~~'/o~~~~~~.ot what is intended to be 

~~·J.~~~~~·~~r)t.~~. 

communicaiied~ For ~ple, a clear photograph consisting or a representation 

or a bank drat't may, in its enciphered or cryptophotographio form, as produced by the invention, consist of an absolutely unsymmetrical, very much 

disordered hodge podge of lines, points, or spots, conveying no idea whatsoever, least of all, that it represents a bank drat't. 

(( ,, 

Equivalent to the phrase key text as employed in cryptography, 

l\. " the phrase key photograph will h~re be used in referring to the photograph 

or printed, hand-drawn, or typewritten material that is employed as the 

key in enciphering the clear photograph. And just as it is essential that 

both correspondents in the ordinary methods or cryptographic communication 

possess identical le.eye, so it is necessary, in accordance with the requirements of this invention, that the correspondents possess identical copies 

or the key photograph. And just as in any scientifically constructed 

system or cryptography the essence of the secrecy achieved by the system 

is inherent not in the method (which may be kn~ to all persons) but in 

the specific key that is em.ployed (which is known only to the correspondents and is readily variable),ao in the system contemplated herein, the 

secrecy features are inherent in the use of a key photograph which is known 

only to the correspondents and which is readily changed, perhaps with each 

J_ 
REF ID:A1051~ 

clear photograph to be enciphered. 

The various objects and features of the invention will be clear 

from the following detailed description. and accompanying drawings. 

Figure 1 to 6. 

Figure 1 shows a portion of a circuit at a transmitting station, 

this portion containing the fundamental elements of our invention. 

Figure :l. shows a portion or a circuit at the receiving station 

for interpreting the signals transmitted by the sending station. 

Figure 5 shows a specific embodiment or our invention in a transmitting station. 

Figure 6 shows a corresponding specific embodiment in a receiving 

station. 

Figure:J shows a very much enlarged scale minute portions of three 

lines, the first occurring in a clear photograph to be transmitted; the 

.· second, a line occurring in a key photograph, and the third representing 

the resultant effect of the combination or the electrical equivalents·of 

the first and second lines, and constitutes the resultant line or the 

oryptophotograph. 

Figure 4 shows in a form corresponding to Figure 2, a set of 

lines, the first being the line in the oryptophotograph as actually re-

· ceived; the secon~, the line in the key-photograph identical with the 

homologous line at the transmitting station; and the third, the line re4 
• REF ID:A1051 • 

sulting from the combination of. the electrical equivalents of the first 

and second lines. yielding a negative copy of the line in the original 

or clear photograph. 

> 

In these drawings only those parts which are essential to the 

exposition of our invention are shown. It will be understood that the invention is readily applicable to any of the present methods and systems 

of space or wire radiophotography. The essential features of all systems 

are .that the picture or material to be transmitted is analyzed into a 

si~gle sequence or very small light and dark points; means is provided 

for translating. transmitting. and receiving these light and dark points 

into and by some characteristic of an electric current; and at the receiving 

end means is provided for reversing the process. that is. for translating 

the received electric signals into light and dark points corresponding in 

relative values and positions with those of the orif,inal picture. In 

nearly all practicable systems of today the analysis referred to involves 

the use of a photoalectric cell which is rapid in its response to changes 

in intensity of lifht actine uron it. The exact form which the process 

of photo-analysis takes in the praticular system of radiophotography used, 

that is. the mechanical arrangement for producing the sequence of changes 

in the properties of an electric current corresponding to the lieht and 

-5-
REF ID:A10515. · 

dark points of the picture, is of no direct concern in the present invention. We shall first merely begin W:ith the photoelectri~ cell and its 

associated electrical circuits, and troat of the electric currents controlled by the cell, leaving it to be understood ·that such other mechanical 

and electrical arrangements.as are essential to the complete analysis or 

the picture at the transmitting end, and its synchronous synthesis at the 

receiving end, really do not fall properly within the scope or.the invention 

and are immaterial to its exposition. However, at a lat~stag~, for 

purposes of illustration, our invention is shown embodied in one of the 

most successful of' the present day systems of radiophotography. 

Reference will now be made to Figure 1. In this figure are shown 

within broken lines the four principal sections of' apparatus and circuits 

comprising the essence of our invention. Using the terminology set forth 

above. A represents the apparatus and circuits involved in producing the 

sequence of signals corresponding to the light· and dark point analysis or 

the clear photograph. A comprises B, a photoelectric cell of the well 

known two electrode type; c, a three electrode vacuum tube amplifier of 

well known form; D, a two or three electrode vacuum tube rectifier, also 

of well known form. The polari·Ues of the currents issuing from D are as 

indicated in the figure. In the same figure, A1 represents the apparatus 

-6-
REF ID:A10515 • 

• 

and circuits involved in producing the sequence of. signals corresponding 

to the light and dark point analysis of the key photograph. A1 compriRes 

Bl, cl, e.nd Dl, all essentially identical in form and operation with the 

corresponding parts, B, C, and D of A. The polarities of the currents 

issuing from nl are as indicated in the figure. 

For purposes of ease in reference, that. section of Figure 1 which 

is indicated by the letter E will hereafter be designated as the "interaction 

oircuit11 , 111herein the electrical signals emanating from D and nl interact 

or combine to produce a single signal as the effect of two conditions 

existing sinmltaneously in A and A1• Interaction circuit E consists of 

two equal sections, F and Fl, having one side, H-Hl, in common. I is a 

winding situate at· the midpoint of. H-Hl. II is a winding in which currents 

are induced by the passage or current through I. J and Jl are adjustable 

resistances, the purpose of which is to permit of the establishmant of a. 

: 

).., 

state of complete electrical equil/brium. between sectio~s F e.nd Fl of E, 

so that if impulses of equal potential come from D and nl simultaneously 

they exactly cancel each other and therefore no current will flow through 

winding I as a result of the interaction of the two signals. Results of 

other conditions existant momentarily in interaction circuit E will be 

discussed later. 

-7-
REF ID:A1051~ 

Th~ signals induced in Il are led to K, hP.reaf't~r designated as 

the "resultant circuit". K r.omprises L, a multistage amplifier of well 

known form, M, a modulator or N, a sour~e of carrier oscillations preferably of the power tube type. The eloctrical oscillations coming from K 

are then led to line or ~o a transmitting antenna. 

It is to be understood that the analysis of the clear photograph 

and the key photograph occurs simultaneously. This may be effected by 

having appropriate mechanical arrangements. In the case where the photograph is mounted upon a rotating cylinder which is horizontally displaced 

past the analyzer photoelectric cell, the cylinders bearing the clear 

photograph and the key photograph can be made to rotate synchronously by 

gearing to the same drive shaft, and similarly the horizontal displacements 

of both can be made cynchronous by a common driving member. In the case 

where the analysis of the photograph is effected by keeping the photograph 

in a fixed position and causing the analyzer to make the necessary excursions over the surface of the photograph, the excursions of the clear 

photograph and the key photograph analyzers can be me.de synchronous by 

appropriate mechanical arrangemAnts. It is only necessary that when the 

· . . analyzer is at a specific point in one photograph it"should be at a homo• 

J.ogous specific point in the other. 

Let us now consider the operation of the circuits described, and 

-e-
··. 

REF ID:A10515. 

for the present. we will consider that both the olcar photograph and the key 

photograph consist of pure black line "positive" transparencies, all their 

lines being of equal intensity or blackness. There can be but one of four 

and only fuur possible cases of conditions existing at a given moment in 

two homologous points in the clear and the key photographs simultaneously. 

The four ca~es are ·as follows: 

~ A bl~ck point in the clear photograph ~ ~~ ~ 

( A black point in the key photograph 

( A black point in the clear photograph ,, .. .. 2. ( 

( A white point in the key pho~ograph 

( A "Ythi te point in the clear photograph 

3. ( 

,, " .. ( A black point in the key photograph 

" .. ( A. white point in the clear photograph 

4. ( 

( A. white point in the key photograph 

It will be. assumed that a black point in either photograph prevents or cuts off the light playing upon the photoelectric cell so that no 

current flows through the cellj only when the light falls upon it does current flow through it, in proportion to the intensity of the light. Having 

assumed that we are dealing now with pure black line material, it is 

obvious that a black point represents a period of no current, a white point, 

one of current flow; in short, the s·ignals in this case partake of the 

nature of •spacing• and "marking" impulses..;... ~a~· 

-9-
REF ID:A10515. 

Hence, taking case (1), where two black points occur simu.lt.aneously, no current will flow· through either D or nl, and hence interaction circuit E will remain unaffected; no signal •rl.11 be produced in the ·resultant 

circuit K. Taking case (2), where a black point in the clear photograph 

and a white point in the key photograph occur simultaneously, let us see 

what happens. ~he black point in the clear photograph allows no light to 

reach photoelectric cell B, and hence will cause no change in A, and no 

signal will issue from D; the white point in the key photograph will, however, allow light to reach photoelectric cell Bl, and hence cause current 

to flow through Bl; thence it is ampl.if'ied at cl, and rectified at nl. 

A positive impulse starts at ol, flows along P1to point H. Photoelectric 

cell B being in the nature of a key which opens and closes a circuit, and 

the circuit through A being at this moment in the open condition, the 

current at H cannot.:rlow along Q, but can along H-Hl, passing through winding I, thence along Q1 b'ack to negative terminal R1 or n1• A circuit has 

been completed and the flow or current through I causes a current to be 

induced in Il, which is then amplif'ied in L, end causes the modulator U to 

... !AS'lld~ 

send out a.,sir,nal along s,sl. The result, then, of the interaction of the 

electrical conditions representing a blank point in the clear photograph 

and a white point in the key photograph is that a signal is produced in 

the resultant circuit K, and transmitted at s,s1• 

-10-
REF ID:A10515. 

Case (3) is merely the interchange of the separate conditions 

set forth under case (2), and will likewise result in the production of a 

signal at s,sl. 

In case (4) we have the condition where a signal is set up at D 

and Dl simultaneously. A positive impulse starting at O in A flows along 

P reaching H1; a positive impuls·e of equal potential starting at ol flows 

along pl reaching H; the two equipotential currents arriving at the terminals of H-Hl simultaneously, but going in opposite directions exactly oppose 

each other; or, looked at in another way, H and Hl will be points of equal 

• 

potential· and hence no current will flow through the conductor oonneoting 

them. Thus, no current can flow through I, hence none is induced in Il, 

and no signal is produced in K. 

It is clear, therefore, t.hat the four cases set forth abovo result in only two ultimate conditions: a signal is either produced or not 

produced at s,sl. These signals may be transmitted along conductors according to the principles of wire radio, or may be emitted from an antenna, 

according to the principles of space radio. The transmitted signals represent or rather correspond to the cryptophotograph transmitted. 

In Figure 2 there are illustrated examples and the results of all 

four cases specified above, in the form of theoretical photomicrographic 

dit.~ram•h Here A repreoents a section along a portion of the "positive" 

-11-
REF ID:A105159 

clear photograph, with the black and white portions represented as indicated by a to m. Al represents a section along a honologous portion 

of the "positive" key photograph, and it is to be understood that superimposed parts or A and Al, a to m and al to ml, represent points subject 

simultaneously to the scrutiny of the analyzing photoelectric cell. K 

represents the sequence ·or resultants in the form of a succession of 11 011 s 

and ''i"s, where 11011 represents "no signal" and "f" represents "signal". 

If' these resultants were received and recorded directly on a film, ·and it 

it were possible to transmit any kind of a signal without some losses, 

causing the rounding oft of the signal, the received and recorded cryptophotograph would appear as shown at s, Figure 2. The rounding oft of the 

signals, however, is of no direct concern in the present invention and 

will be disregarded. 

The superimposition of a ot A and al of Al represents case (l), 

a condition where no signal is produced because no currents flow through 

the clear photograph and key photograph currents of Figure l. The resultand, all of K, is therefore a blank, and it such a cryptopho~ograph were 

being recorded as such, at the receiving end, no light would be directed 

I 

on the recording sensitized surtaot. In case the sensitized surface were 

a film negative, on development the particular point under discussion 

would be blank, that is, transparent. In case it were a sensitized paper, 

·-12-
on development, the point would be white, as shown in alll of' s. Tho 

superimposition of e of A and el of Al represents oase (2), a condition where 

a signal is produced at K of Figure l~ The resultant, ell of K, in Figure 2 

is therefore a 11 .J.11 and represented by a black point in elll of s. The 

superimposition of b of A and b1 of' A1 in Figure 2 represents case (3), a 

condition where a signal is produced at K of Figure 1. The resultant, bll 

of K, is therefore a 11 11 , represented by an 11 exposed" or black point, blll. 

Finally, the superimposition of g of A and gl of Al represents Case (4), a 

condition where no signal is produced at K of Fie;ure 1 because the currents 

established at D and nl of .Figure l exactly neutralize each other in the 

int~raction circuit E, and hence bll is an 11 011 and is represented by blll, 

a transparent or white point. 

It may be pointed out that the cryptophotograph produced by the 

invention is totally dif'f erent from the photograph produced by exposing 

& single sheet of sensitive photographic paper to two different negatives. 

In the latter case there is merely a sort of arithmetical additive effect, 

while the resulting print may be conf'used, yet it is always possible for 

the eye to separatft the constituent parts of each picture, and thus see 

either or both of them. In the. case of the cryptophotograph produced by 

this invention it is altogether different, and there is no mAre arithmetical 

-13-
e REF ID:A10515.' 

additive effect. It is a sort of algebraic additive and subtractive effeet so that the resultant bears no resemblance to either the clear or the 

key photograph. 

In Figure '.3. are' shown the arrangements of parts and circuits at 

the receiving station, suitable for receiving and simultaneously deciphering the cryptophot.ograph. It is to be understood that. synchronization of 

the transmitting with the receiving station is necessary to the practical 

operation of the present invention just as it is in the ordinary systems 

of radiophotography, and the methods well known in the art are applicable. 

In the more successful systems the receiving station is under the complete 

control of the transmitting station, which exercises the primary control. 

In Figure 2, Al, with its parts Bl, cl, and nl, is exactly the same as the 

corresponding parts of Figure 1, and it is or course essential that the key 

photograph employed to decipher the recei~ed cryptophotograph must be identioal with that employed at the transmitting station to encipher the clear 

photograph. All represents the received cryptophotograph circuit, where 

s,sl represent the ter:nll.nals of the incor.iing signals, ell is the amplifier 

and oll the rectifier, all c£ well known form, suitable for the reception 

of th~ signals corresponding to the transmitted cryptophotograph. E of 

Figure 1 is the_ same and functions for the same purpose as E or Figure l; 

its coils I and I 1 are similar to the corresponding coils of Figure l. K1 

-14-
• REF _ID:A10515 • 

ie the resultant circuit, where the electrical resultants of the interaction circuit E are amplified by L1 and than caused to retranslate the 

electrical signals into light values by the light value M.l which controls 

the source of light, Nl. ul may be or the magnetic type or of any other 

form suitable for translating the electrical signals back into their cor-

• 

responding light values and ma.king a record of the same on sensitized paper 

of film moving synchronously with that at the transmitting station. 

The interaction circuit El or Figure ,_functions exactly as does 

E of Figure 1, so that further description is necessary toward an understanding of the principles. In the resultant circuit Kl, Figure 2, the 

light value M1 t&.kes the plaoe of the modulator M. of Figure 11 and ~auses 

a record to be made of the resultants of the interaction between signals 

arriving from the distant station, led into the interaction circuit E from 

nll of All, and local deciphering signals led into the interaction circuit 

The four cases detailed in connection with the sets of conditions 

in the interaction circuit of the transmitting station, Figure 1, are identical in form with those at the receiving station, Figure 2, but the resultant effects in the resultant circuit are exactly opposite. ifhereas at 

the transmitting station the simultaneous occurrence of a white point on 

both the clear photograph and the key photograph represents a period of 

-15-
REF ID:A10515. 

current flow to the i~teraction circuit, but a period or no current flow 

in the resultant circui·t, at the receiving station the simultaneous occurranee or a period of no current flow in the receiving half ot the interaction circuit and a similar period of current flOW' in the local or deciphering half of the interaction circuit causes current to flow through 

I of the interaction circuit,, thence through I 1 of the resultant circui't.,, 

and hence causes light to fall on the recording or sensitized surface of 

the deciphering cylinder. If this recording surface is· a negative film,, 

the particular point under discussion would be exposed to light; on developraant the point would be black. By contact printing on sensitized paper, 

however, the black point v1ould be reversed to a white point, azid thus made 

to correspond exactly with the point on the clear phot~graph. 

In Figure 4 there are illustrated examples and the results of all 

four oases of interaction, in a form similar to that shown in Figure:2. s1 

represents the received cryptophotograph, if recorded. Kl shows the 

sequence of incoming signals representing the received cryptophotograph,, 

corresponding in its sequence of 11 0 11 s and "t''s with that of K of Figure 2. 

Al represents a section along that portion or the key photoeraph which is 

necessary properly to decipher the particular section or the cryptophotograph 

under discussion: A1 of Figures ~ and 4 are, as stated before, identical 

in whole and in part, and the synchronizing mechanism must,, of course, 

-is-
REF ID:A10515. 

bring pomologous parts of both key photographs into the correct.positions 

in order to maintain the proper enciphering-decipherin~ relationship be-

· tween the transmitting and the receiving stations. All or Figure 4 represents a section along the resultant or deciphered cryptophotogram, which, 

if correctly done, is a negative image of A of Figural, the original or 

.c.lear pho~ograph. A of Figure 4 is the positive print of All, and corresponds exactly with A or Figure 3. 

In Figure 4 the interaction of alll of Kand.all of A1 represents 

J 

case (l),· a condition where no signal is produced. 'l!he resultant in this 

case is shown by a of All, Figure 4, a blank or white spot. It is thought 

unnecessary to detail examples of the other three cases, because they are 

exactly a.na.log~s to those already explained in connection with Figure:i • 

.. • 

It is only to be pointed out that the deciphering process results in the 

production of All, which is an exact duplicate of A of Figure 3, the origi-

· nal or clear photograph, except that it is a negative of A. By contact 

printing or by enlargement from the developed film, A, the exact clear 

photograph is reproduced. 

In Figure 5 there is shown in digrammatic form a specific embodiment of the invention in a practical wired radiophotograph transmitting 

station. Here a motor,\Q, is the dtivin~ mechanism of the single shaft 1, 

the rotation of which causes the cyli?ders 2 and 21 to revolve. through the 

-17-
• REF ID:A10515 • 

chronous horizontal displacement of the cylinders 2 and 21 is accomplished 

by means of the movement or identical carriages 6 and sl, and identical 

screw portions 7,71 or the shaft 1. Thus, all portions of the photographic 

transparencies. mounted upon 2 and 21 are brought under the scrutiny of the 

light coming from light sources 8 and 81, through lenscii's 9.and 91; this >.J' 

light is either passed or stopped by portions of the photographic transparanoias, depending upon whether a light or a dark portion, respectively, 

appears under the focal p~int of the l9nses 9 and 91. B and Bl a.re the 

photoelectric cells affected by the light passing through thP. photographic 

transparencies. No further explanation of the apparatus com.prised with in 

the dotted sections A,Al, E and K ia necessary inasmuch as they cor~espond 

exactly with similarly labeled parts in Figure 1. 

The motor 10 in an impulse motor of well known form, controlled 

by an electrically operated tunin~ fork, 11. The motor 10 drives the shaf't 

l through a clutch meoh~nism, 12, which is controlled by a local switch 

and which at the momont of engagement sends an impulse along conductors 

13,131 to the amplifier L, whereupon a signal is sent to the receiving 

s~ation, and the starting clutch at the distant end is operated to start 

the shaft which drives the homologous receiving cylinders there to revolvo at the srun.e instant that the drivo shaft 1 starts to revolve at the 

-18-
REF ID:A10515. 

transmitting station, Figure 5. 

Impulses from the control or synchronizing carrier wave oscillator 14 are controlled by modulation by the master fork 11, and the 

synchronizing impulses are sent to line s,sl through a control channel 

filter, 151, and a terminal amplifier, 16. The frequency o£ the control 

carrier oscillations in order to permit of the transmission of both 

oscillations over. one channel, and hence the filter circuits 16 and 161 

are inserted, in order that the two modulated currents may be kept separated from each other. 

The terminal amplifier 15 is necessary in order that signals of 

sufficient strength may be sent to line or to the transmitting antenna • 

• 

The oper~tion of the clear photograph circuit A, the key photograph circuit A1, the interaction circuit E, and the resultant circuit K 

is exactly the same as has been described in connection with Figure l, 

and nothing further need be said concerning it in connection with Figure 5. 

In Figure 5 there is shown in diagramm.ation form the arrangements 

at the receiving station. They are self-explanatory when considered in 

connection with Figures 'a. and 5. The incoming signals on the line s,sl 

are first amplified in 16. The electrical filters 15 and 161 serve to 

separate the two modulated carrier frequencies from each other, that 

appropriQte to the picture system being separated out by the picture 

-19-
REF ID:A10515. 

channel filter 15, that appropriate to the synchronizing or control 

system, by 151. 

The isolated modulated picture carrier is then amplified in ell, 

and rectified in nll. The isolated modulated control carrier is amplified 

in Ll, and rectified in ul. Th~ rectified picture currents are then led 

into the interaction circuit E; the rectified control currents are led to 

the secondary fork 111, ~ich controls the motor iol and keeps it in exact 

synchronism with the corresponding motor at the transmitting station. Thus 

the master or primary fork, 11, at the transmitting station not only con• 

trols the motor 10 but also the motor iol at the receiving station through 

its dependent fork 111. 

The starting mechanism 121 is operated by the amplified starting 

signal coming from t~e line s,sl through Amplifier ell, and this signal 

starts the drive shaf't il to rotating exactly at the same instant that draf't 

sha!'t 1 at the transmitting station starts. 

It is to be understood, naturally, that the mechanical arrange• 

ments as regards the rotation and horizontal displacement of the cylinders 

2 and 21 at the receiving station are identical with those at the transmitting station, and that the cylinders are of exactly the same dimensions 

throughout. It is also clear that the key photograph mounted upon cylinder 

-20-
REF ID:A10515. 

21 must not only be an exact duplicate of that at the transmitting station 

but also it must be mounted upon the cylinder in exactly the same relative 

position as its mate at the transmitting statj.on. The requirement in this 

• 

respect is no different from that in ordinary oryptographio processes involving the use or continually shifting key letters; for not only must the 

.enciphering and deciphering sequences be identical but also they must be 

applied at exactly homologous parts ot the text. 

The interaction in E of currents comin~ through Al with those 

coming through All is exactly in accordance with the four cases detailed 

before in connection with_ Figure la The resultant effects are impressed 

upon winding Il and thence they go to resultant circuit Kl where the light 

• 

valve yl is controlled by them. Light valve yl servesl\to ~ open and close 

~AD ~ ;tt:A. ~, Jt ~ ¥°J 

a shutter of the optical system Nl~and thus cause the electrical variations 

of Il to be translated into light variations. The ray or light passes 

thrott.gh lens 9 and impinges upon a sensitized film mounted upon 2. The 

result is that the received oryptophotograph is deciphered and corresponds 

to the original or c~ear photograph at the transmitting station, as a 

negative or the latter. 

In the description thus far the photographs used as matter to be 

transmitted or as keys have been considered to be of pure black line com-

. -21-
• REF ID:A10515 • 

position against a pure white background. This condition is not a 

necessary element to the successful functioning of the invention, which 

is applicable to the enaipherment of photographs of varying densi'l:.y as 

regards 'l:.he lines of which they are composed. 

Referring again to Figure 1,. let us suppose that in the clear 

photograph circuit, A, the analyzer photoelectric cell B is scrutinizing 

a point,, X, and in the key photograph circuit Al, the ~lyzer Bl is 

scrutinizing a homologous point xl. f'urther, let us arbitrarily draw up 

a scale of intensity of shade, calling pure white or perfect _transparency 

.f.l, and pure black or perfect opacity O,, with the gradat:l.ons between the 

two extremes in ten equal steps. Let point X be of opacity .9, and xl 

ot opacity .1. X would then be almost pure white or almost perfectly transrarent; xl would be almost pure black or almost perfectly opaque. Now in 

an alkali metal photoelectric cell the illumination-current relationship 

is rectilinear, that is, as the illumination of the cell is changed the 

current permitted to pass through it changes in direct proportion. Hence, 

the current passir.g through D of A will be proportional to the illumination 

of B, and likewise the current passing through nl of Al will be proport.ional 

to the illumination of Bl. Now ~;.nee point X is of density~9 it will allow 

almost the entire available amount of" light to•tall on B; and since point 

xl is or density.1, ii. will allow very little light to fall on Bl. The 

-22-
REF ID:A10515 .• 

currents produced being proportional to the illumination, the current 

through B, and thence through D,, will be app~oximately nine times as 

much as that through Bl,, and thence through D1• Therefore, there will 

be a difference in potential between Hl and H, thP. form~r being 9 uni~s,, 

the latter only l unit. Hence there will be a flow of current from Hl 

to H t.hroue;h I,, equivalent to 8 units, and the .iPt'Dunt of' flow 'will be in 

proportion to the difference in illumination of B and Bl,, that is, to 

the difference in intensity of blackness of X and xl. The modulation 

.. of the carrier will then be in proportion to the current flowing through 

I, and thus the differonce in light value between X and xl is transl!litted 

ot>er"line s,s1J in the form or a carrier wave modulated in amplitude in 

accordance with the sequence Of resultant effects in I. The case in 

this respect is exactly analogous to that which e;dsts in radio telephony. 

At the receivine; station, Figu.re 2, there will flo~ through 11 

• 

currents representing the rectified signals received, and these will 

vary in potential with the modulations impressed upon the carrier wave . 

emitted from the transmitting station. The currents induced in I 

will then affect the interaction circuit El in the same manner as before 

described. In the case under discussion the flow of current through 

I of Figure 2 is equivalent to 8 units. Thie current will interact 

· with the one originating locally in Al, which as was noted above, is 

equal to that caused by a point xl in the key photo~raph. the density 
• REF ID:A10515. 

value of which is .1. The result of the interaction of the two currents, 

that from the incoming signal, .a, and that from the local deciphering 

signal, .1, is an additive effect, viz., .9, which is exactly equal to 

that of point x· at the transmitting station. 

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