556 
POPULAR SCIENCE REVIEW. 
uses as few as six photographs for his specimens of photo-sculpture, and 
these works must therefore owe a great deal more to the sculptor than to 
the photographer. 
The Chementi Pictures.— The controversy started by Sir David Brewster 
concerning these pictures, and which he advanced and argued from as 
having been executed in the middle of the seventeenth century for stereo- 
scopic purposes, has been recently revived in the pages of the British 
Journal of Photography by Professor E. Emerson, in reply to a letter from 
Sir David published in the Philosophical Magazine for January last, which 
letter was itself a reply to remarks contained in an article in the aforesaid 
British Journal on “The Perception of Relief,” written by Professor 
Emerson. Mr. Emerson states that copies made for him by hand from 
the photographs of these drawings convey an amount of relief neither 
greater nor less than that obtained from the photographs themselves, and 
gives, as illustrative of the ease with which even our much-talked of 
“own eyes” will deceive us, the fact that he has frequently mounted 
“ two identical or right-eye views of the same scene side by side, and 
never failed to get a verdict, even from very skilful observers, that they 
exhibited stereoscopic effect, which was impossible.” The Professor says, 
if Chementi had executed works which must have been such startling 
novelties, it is neither likely that his discovery would have become lost, 
nor that only one specimen of it would have been now in existence, 
although we think both these circumstances might be shown, by historical 
evidence, to be by no means improbable. The supposed stereoscope, 
bearing date 1670, advanced in evidence by Sir David Brewster, is asserted 
to be no stereoscope, and the size of the Chementi drawings, viz., “about 
twelve inches high, by eight and a half broad,” is certainly evidence on 
the side of the Professor. After giving very imperfect woodcuts of the 
drawings, and advancing the publicly expressed opinions of various 
gentlemen in support of his views, Mr. Emerson w*inds up with a long 
series of measurements, which, taken in conjunction with the principles 
governing the perception of solidity, at least show that if these drawings 
were intentionally stereoscopic, their execution could not have been based 
on such scientific calculations. Our own opinion of this controversy is 
simply that it is a very useless one, because the evidence on either side is 
insufficient for the formation of any specially useful or important conclu- 
sions. 
PHYSICS. 
Spectroscope for Stellar Investigation.— Professor Miller and Mr. Huggins 
recently presented (May 26) a valuable paper to the Royal Society upon 
the spectra of some of the fixed stars, and employed in these researches an 
instrument of the following description : — In the construction of the spec- 
troscope a plano-convex cylindrical lens, of fourteen inches focal length, 
was employed to convert the image of the star into a narrow line of light, 
which was made to fall upon a very fine slit, behind which -was placed an 
achromatic collimating lens. The dispersing portion of the arrangement 
consisted of two dense flint-glass prisms, and the spectrum was viewed 
