Editor's Note: This story is a supplement to the "50, 100 and 150 Years Ago" column from the August issue of Scientific American
The problem of tele-vision has long been a favorite one with enterprising inventors. The many telephotographic apparatuses which have been made known in the course of the last few years are the outcome of their endeavors. But the transmission of photographs, drawings, and handwriting over a telegraph wire is incomparably more easy than the instantaneous rendering of the moving objects situated at the transmitting station.
It is true a solution of the problem could be attempted on the very principle underlying the construction of these tele-photographic apparatuses. the various sections of a picture would be produced--not successively, as in the case of tele-photography, but simultaneously, as well as instantaneously, without any lag, and would become visible immediately without any photographic process. There are two difficulties in the way of a practical realization of this idea, viz., (1) the extraordinary costliness of such an outfit; (2) the sluggishness or inertia of the vital organ of most systems, viz., the photo-electric selenium cell.
Mr. Ernest Ruhmer, or Berlin, well known for his inventions in the field of wireless telephony and telegraphy, has succeeded in perfecting what is probably the first demonstration apparatus which may be said actually to solve the problem. The writer has had an opportunity of inspecting this curious machine immediately before it being sent to Brussels, in order there to be demonstrated before the promoters of the Universal Exhibition planned for next year. In fact, a complete and definite television apparatus, costing the trifling sum of and a quarter million dollars, is to be the clou of this exposition. The demonstration apparatus has been produced at a cost of $1,250, and by reason of its more elementary construction, lends itself only to the reproduction of the pattern, consisting of squares arranged in different combinations.
The pattern is thrown on a screen hung on a wall, which screen is a square divided into 25 square sections. Behind each of these sections is arranged a highly sensitive selenium cell in which, by a novel process, inertia has been eliminated so far as possible. It thus responds instantaneously to any variation in lighting it is exposed to.
At the receiving station is arranged a similar screen divided into the same number of sections, each of which communicates with the corresponding section on the transmitting screen. while the actual system used in transmission is kept secret, this much may be stated, that a highly sensitive mirror galvanometer reconverts the fluctuations of current produced by fluctuations in luminous intensity on the transmitting screen, into corresponding light-variations. An accumulator battery supplies current to the tele-vision circuits.
As soon as a perforated pattern is inserted in the projector, a telegraphic reproduction of the picture appears at the very moment it is thrown on the transmitting screen. The sluggishness of the cells has been overcome to such a degree that the telegraphic picture will respond practically instantaneously to any motion. In fact, a reproduction obtained at most in a few minutes with the photo-telegraphic apparatus so far constructed, is here achieved in fraction of a second, so that several phases of a motion can be reproduced within a second.
It is hard to realize what an amount of laborious work has been expended in constructing even this comparatively simple apparatus. In fact, each section, with its selenium cell and mirror galvanometer device, is an instrument of precision in itself, while the final apparatus will be composed of 10,000 elements of the same kind. Each selenium cell will have to wound personally by the inventor, who never intrusts this work to anybody else.