108 Mr. J. Elliot on two new Forms of the Stereoscope. 



vertical axis until it gives a full view of the picture furthest from 

 it. All these arrangements must be carefully effected before any 

 attempt is made to unite the pictures. Finally, when that is 

 attempted, if the one picture appear a little to the right or left 

 of the other, turn one of the telescopes on its vertical axis till 

 the pictures come together ; but if one of them appear a little 

 higher than the other, raise or depress the one telescope by means 

 of the small screw beneath it. 



To this form of the instrument, which is evidently the more 

 perfect of the two, I have proposed to give the name of the 

 Telescopic Stereoscope. 



Since these forms of the instrument were designed, Mr. Water- 

 ston has suggested a simpler contrivance to serve the same pur- 

 pose as the first, although more like the second in appearance. 

 It consists of two tubes, used in the same manner as the two 

 telescopes, and either held separately in the hands, or connected 

 in the same manner as the telescopes. If the tubes are made of 

 the proper length and width, they serve the purpose nearly as 

 well as the box form of the instrument, but have not, of course, 

 the advantages afforded by the telescopes. They may be made 

 with the ends next the eye narrow, and the other ends wider, 

 and capable of elongation, so as to give the necessary proportion 

 of length and breadth. 



Having finished the description, I return again to further 

 limitations of our claims as to novelty. There is no novelty, of 

 course, in the fact of uniting binocular pictures by the eye by 

 cross vision ; and the proper method of doing so, by interchanging 

 the places of the pictures, has been described by Sir David Brew- 

 ster. It was, in fact, his remarks on the subject that suggested 

 my idea of the first-mentioned form * of the instrument for small 

 pictures, which Mr. Watcrston's observation induced me to apply 

 to large pictures. Whether large photographs had been previ- 

 ously treated in the same way by the unaided eye I am uncer- 

 tain. But it matters not : no claim of originality is made in 

 regard to that. The object of the instruments is to facilitate 

 that which undoubtedly the eye can accomplish without them, 

 but less easily and less perfectly. 



It must be mentioned also, that Professor Wheatstone united 

 pictures by the use of tubes, as Mr. Waterston has done ; but I 

 am not aware that he ever did so by crossing the lines of sight, 

 and without that it is impossible to unite large pictures. 



The telescopic instrument, as I have made it, is evidently 

 susceptible of minor improvements. The most useful alteration 

 would probably be to render it available for the double purpose 

 of a stereoscope and an opera-glass. 



* A distinct form from that construced by me many years ago. 



