Henry SUTTON, "Tele-photography",
The Telegraphic Journal and Electrical Review,
November, 7 1890.
[Une traduction en français de l'essentiel de cet article se trouve dans l'article de E.R., "Le problème de la téléphanie, d'après M. Henri Sutton", La Lumière électrique, Paris, 13 décembre 1890]. Voir l'article sur Henry Sutton.
UNDER various names the problem of transmitting optical images by aid of the telegraph wire has at different times had attention drawn to it.
In putting forward something new in this direction, I will begin by inventing a new name, and propose calling the subject Telephany, and the electro-optic instrument the Telephane.
The art of telephony is simple compared with that of telephany. In the former we deal with a consecutive series of waves of varying rate and length, and it is the consecutive character of sound waves that lends itself so admirably to electrical translation.
In telephany we are met, at the outset, with a great preliminary difficulty, having to deal with a surface or plane in which the effect appealing to the brain must be observed in all the varying character at one and the same time.
The problem stands thus : a means has to be devised whereby the varying effects on a plane surface are translated into consecutive series of electrical currents, and by means of the consecutive series of currents reconstruct, so to speak, a copy of the original surface ; that is, we have to take an optical image, seen as a surface, translate it into a line of consecutive varying electrical currents, and by means of these produce an effect as a surface, having the characteristics of the original image.
We have here two images as surfaces having no time value, and a series of electrical currents having a time value, yet these opposing characteristics are to be presented to the brain as a momentary impression.
Before showing how this apparently impossible problem may be handled, I will explain a probable means for electrically transmitting a photograph.
If we make what photo-mechanical operators call a screen negative of a portrait, using a coarse screen, and from this a photo- lithographic transfer, transfer it to zinc, and transmit the result by any of the several autographic systems, we have the desired result. In fact, if we apply our knowledge of half-tone block making to telegraphy, we are at once in possession of a means of electrically transmitting the photographic semblance of any person.
We may make a screen negative, and from that obtain a print on zinc or copper coated with sensitive albumen or bitumen, using the usual solvents, water or turpentine, as the case may be, with which to wash away the unexposed albumen or bitumen, then let the stylus of any autographic system traverse the developed image, the result at the receiving end is a facsimile portrait. I have used the expression screen negative, as it is an understood trade name ; as a matter of fact, a screen positive would be necessary. We may go further, instead of receiving the facsimile on chemically-prepared paper, as in the Caselli autographic telegraph, we can make the receiving stylus perforate thin paper (with the electric spark) by means of a constantly- working induction coil, but only put into the receiving circuit by the transmitted current. Place this paper on a lithographic stone or zinc plate, pass a roller charged with greasy ink over it, and we have a printing surface the portrait being transmitted and reproduced.for the printer, photo-electro-mechanically.
But this is not telephany ; the latter must be understood as the means of transmitting images which may be in motion, as seen in a photographic camera, but not in colours.
Having spent some years in studying the problem, I designed the following system five years ago, as my Victorian scientific friends can testify. It may be of much assistance to workers In this direction. I think it offers a fair approximation to the solution of this very difficult problem ; at any rate, if in its present form it is not the actual solution, I feel sure it is in the direction indicated by my method, that the successful accomplishment of telephany will result.
L (figs. 1 and 5) is a photographic objective of the rapid type, producing an intensely illuminated aerial image at A A.
D D (figs..1, 2 and 5), light metal disc revolving at a fixed rate of not less than 650 revolutions per minute under the control of La Cours's phonic wheel and fork apparatus as in the Delany multiplex system.
G. (figs. 1, 3 and 5), a glass or other insulating plate, to the front surface of which is held, by binding terminals, s¹ s, two triangular pieces of metal just separated from each other, E E.
C (figs. 1, 3 and 5), a small piece of lamp-black, selenium or other substance, the resistance of which may be varied by heat or light. Lamp-black compressed is probably the most suitable.
The disc, D D, has a series of small holes, 1, 2, 3, 4, 5, 6, 7, 8, perforated in it, and gradually approaching its centre, as a spiral, these holes must be numerous, and yet only one at a time in the field of the image at A A.
R L (figs, 1 and 5) is the most important part of the transmitter. This I term the regulating lens; it is a lens placed with its plane surface just to receive the aerial image from the objective L, its focal length being such as to bring all rays reaching it through the perforated disc to a point or focus at C, and therefore its function is to introduce them consecutively to the circuit comprised in S¹ E¹, C, E, 8.
Under the influence of this regulating lens the whole image, A A¹ is allowed to act in consecutive manner, and therefore vary the resistance of C in accord with the lights and shades of the original. We thus solve the big problem of translating the plane image into a line of consecutively varying strength of current, and by bringing C under the influence of the whole image within one-tenth of a second, and during the same time reconstruct our image at the receiving station, persistance of vision will enable us to see the image as one impression.
S¹ (figs 4 and 5), any artificial source of light, a beam of which is by means of lens, L, passed through a pair of Nicol prisms, P, A, this beam reaching lens M¹ if; magnified and received by the eye-piece, M, M, and viewed by the eye, E. It is absolutely requisite this beam be received by the eye through optical means. The presence of a translucent screen at X, X, would be fatal, owing to the delicate nature of the desired effect.
D D (fig. 4), is a perforated disc, similar to and revolving synchronously with the disc in transmitter.
K K (figs. 4, 5 and 6), terminals inserted in glass and having a small space between, holding a drop of bisulphide of carbon, S.
On rotating the Nicol, P, 45°, we reach the position of extinction.
The terminals, K, K, being placed in the secondary circuit of the transmitter - that is, to line - the variable electrostatic strain produced in the drop of bisulphide of carbon under the action of induced currents received from transmitter, is to produce variable rotation of the polarised beam, and, therefore, variable quantities of light reach the eye, E.
It is obvious the varying tints will be seen in similar position as in original image, owing to the synchronous movement of the discs.
The receiver is, then, based on Dr. Kers's discovery of the rotation of a plane polarised beam of light, through electric stress producing a strain in the medium.
There seems to me no question that the electric impulses will do their work within one-tenth of a second, and the point is whether the stress at O O will be sufficient to produce an observable effect, and whether this may be increased by passing the light through a bisulphide of carbon cell having a longer path of, say, 1/16th inch diameter, as shown at fig. 6, instead of through the drop of bisulphide; so that, conceding the telephane is based on a rightly conceived principle, it becomes a question whether the quantitative results of the physical effects utilised in its design are sufficiently great.
I think the transmitter may be considered as near the right thing as the present state of our knowledge will admit us to reach ; there is an appearance of finality about it.
With regard to the receiver it is a question of degree : the actual quantity of light required to reach the eye may be very small when received optically ; in fact, so small as to have no power of illumination on a translucent screen ; but a quantity of light producing no visible effect on any media, when received by means of an eye-piece shows a bright disc. Owing to being away from references, I regret my inability at the moment to give the name of the inventor of the revolving disc ; with the exception of these discs the whole design is original, and was devised at Ballarat, Victoria.