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XVI. On two neiv Fo}-7ns of the Stereoscope, intended for the 

 purpose of uniting Large Binocular Photographic Pictures, by 

 James Elliot, Teacher of Mathematics, Edinburgh ; and on a 

 third Form of the same Instrument, for the same purpose, by 

 George ^Vaterston, Stationer, Edinburgh^. 



IT may be rash to annouoce as new any form of an instrument 

 in exhausting the varieties of which every eflbrt of ingenuity 

 has ah'eady been employed, and on which, it may be said at pre- 

 sent, literally as well as metaphorically, the eyes of the nation 

 are fixed, so that we cannot tell what a day may produce, or 

 what it may already have produced. I therefore advance the 

 claim with all due hesitation, and with the distinct proviso that 

 novelty is asserted only as far as our own knowledge goes, and 

 the knowledge of others to whom the instruments have been 

 shown, and only so far as I shall further limit the claim in the 

 following description. 



To commence that limitation, then, there is no novelty in the 

 mere fact of uniting large binocular pictures. Professor Wheat- 

 stone's instrument does that; but for such pictures it is liable to 

 several objectionsf. In the first place, according to his method, 

 the pictures must face each other ; and w hen large, they must 

 be placed a long way apart, so that they cannot easily be attached 

 to the instrument ; consequently you must either put up sup- 

 ports for both, or hang them on opposite walls of the same room, 

 at the risk of finding these at an unsuitable distance, unequally 

 illuminated, and subject to other inconveniences. Secondly, 

 there is some trouble in placing them exactly parallel. Thirdly, 

 if the instrument is not placed precisely equidistant from the 

 two, the one will appear larger than the other, and they wdl 

 refuse to unite. Fourthly, there is a considerable loss of light 

 in reflexion. Fifthlj', a double image is formed by the two sides 

 of the glass, the separation being rendered more conspicuous 

 from the oblique angle at which the mirrors are placed. 



It is not, however, as rivals to Professor Wheatstone's instru- 

 ment that these are introduced by us, but simply as furnishing 

 other modes of attaining the same result; and, in fact, they 

 have been brought out almost accidentally, and without any pre- 

 conceived design at all. It will therefore probably be best to 

 introduce the description of them by giving an account of their 

 origin. 



A few weeks ago, Mr. Waterston happened to have in his 



* Communicated bv Mr. Elliot ; having been read to the Royal Scottish 

 Society of Arts, Jan. 12, 1856. 



t I mention these objections rather from the statements of others than 

 from my own knowledge, never having used Professor Wheatstoue's ste- 

 reoscope, and having only once seen it. 



