536 Mr. T. S. Davies on Geometty mid Geometers. 



have identically the same motion. This last condition is easily 

 fulfilled, by fixing on a common axis furnished with a single 

 winch the two toothed wheels intended to turn the lower pinions 

 of the two steel rods. 



Only one real difficulty presents itself, but it is considerable ; 

 this is to construct the figures of the two discs in such a manner 

 that those of the one should have with those of the other the 

 precise relation which the stereoscope requires. Nevertheless 

 this may be surmounted, by employing a process for which we 

 are also indebted to the inventive genius of Mr. WTieatstone. To 

 obtain a couple of drawings ada])ted to give, in the stereoscope, 

 the representation, not of a simple perspective in outline, but of 

 an object having rounded forms, such as a statue, and that with 

 the shades and lights, Mr. ^Vlieatstoue conceived the idea of pro- 

 curing, by means of photography on paper, two projections of 

 the object, by placing successively the photographs in two differ- 

 ent positions, so that the two projections should have between 

 them the necessary relation. Now we might have executed in 

 plaster, for example, the models of the sixteen modifications of 

 the regular figure, the image of which it is desired to produce 

 in the combined apparatus under consideration ; then take by 

 means of the photographic apparatus a pair of drawings of each 

 of these sixteen models ; and lastly, place these drawings after 

 suitable distortion on the two discs. Without doubt this would 

 be a tedious operation, and one which would require great care ; 

 but we shoidd be amply recompensed by the marvellous nature 

 of the residts. 



LXXVI. Geometry and Geometers. Collected by the late Thomas 

 Stephens Davies, F.R.S.L. H^E. ^c* 



No. VII. 



IN the year 1821 an unpretending volume issued from a local 

 press (Liverpool), entitled " Geometrical Amusements, or a 

 Coiu'se of Lessons in Construction and Analysis, by J. H. Swale.'' 



* Communicated by James Cockle, Esq., M.A., Barrister-at-Lavv, who 

 adds the following note : — 



[" Since the death of my lamented friend, her late husband Prof. T. S. 

 Davies, Mrs. Da^nes has foi-warded me the above manuscript, his autogi-aph. 

 In sending it to the Editors of the Philosojjhical Magazine for publication, 

 I take the liberty of informing the readers of that Joui-nal that several 

 notices respecting Professor Davies have recently appeared in print, among 

 which I may mention one published in No. 1431 of the Mechanics' Maga- 

 zine; another (by Thomas T. Wilkinson, Esq., F.R.A.S,) in No. 166 of 

 the Architect ami Civil Engineer; and the first part of another (by my 

 brother Dr. John Cockle) in No. 18 of the Expositor. Mr. Wilkinson gives 



