386 
POPULAR SCIENCE REVIEW. 
been very hotly and perseveringly upheld in certain of the photographic 
serials, we were pleased to find in one of them some articles from the pen of 
Mr. A. H. Wall, explaining the grounds upon which they should be dis- 
couraged and denounced. As it is impossible that objects -can ever be cor- 
rectly represented as they are seen by more than one person, or at more than 
one time, the laws of perspective show that to be in strictly accurate drawing 
the representation should be such as one person sees when standing in one 
place, and with the eye at one point of elevation. Now the various portions 
of these “ composition ” photographs almost invariably, and frequently of 
necessity, are taken with the camera in positions relatively different both 
with regard to the height of the lens, the distance of the lens from the object, 
and its position to the right or left thereof. Thus, nothing is more common 
in photographs of this description than to find half a dozen different points 
of sight, nearly as many horizon-lines, and three or four contradictory points 
of distance ; and yet these productions have been awarded medals, and the 
process of thus spoiling a set of good pictures to make that monstrosity 
which violates every rule of art and science, has been upheld as the highest 
aim of photography. 
Plate-cleaning. — Messrs. Walmsley & Co., of Milton Street, Fore Street, 
Cripplegate, have introduced a new spirit called “ Mineral Ether,” which 
they strongly recommend for making photographic plates chemically clean 
with rapidity and certainty. It differs from the ordinary preparations of 
benzole, its specific gravity being ’860, and its boiling-point 170 degrees, and 
by leaving in the evaporation, which is very rapid, no smell. 
PHYSICS. 
A curious Property of Magnetic Oxide of Iron has been demonstrated by 
Mr. Spencer, of Euston Square, in the preparation of his ingenious filters. 
He has shown that the magnetic carbide possesses the power of converting 
oxygen into ozone. Hence the oxide becomes a most valuable material for the 
construction of filters, since by completely burning up or oxidizing all organic 
matters, it renders water pure. Mr. Spencer says its purifying property is- 
“ due to its power of attracting oxygen to its surface,” which then “ becomes 
changed into ozone — or, at least, a body having its properties.” He regards 
ozone as “ oxygen polarized, and considers that oxygen when attracted by the 
magnetic substance becomes polarized, just as a needle is polarized when 
attracted by a powerful magnet. The question, however, may be raised as to 
whether there is such a thing as self-existent polarized oxygen, with little chance 
of a definite answer being received. That the magnetic carbide does ozonize 
oxygen, Mr. Spencer considers to be established by the facts that air passed 
through a layer of it turns tincture of guaiacum-paper blue, as would ozone ; 
that the carbide itself turns the tincture blue ; and that water filtered through 
the oxide into a solution of starch and iodide of potassium renders it faintly 
