NATURAL PHILOSOPHY. 143 



they were printed from engraved copper or steel plates. — British 

 Journal of Photography. 



CHEMICAL ACTION OF LIGHT. 



The interesting researches of Prof. Tyndall as to the action of 

 light on certain vapors and liquids may have no immediate effect 

 upon the practice of photography, but it is impossible to say at 

 what point in his discoveries a practical application may become 

 obvious. Let us illustrate by a speculation upon the possibilities 

 attending his recent discoveries. In his paper before the Royal 

 Society he states that actinic light decomposes the vapor of nitrite 

 and nitrate of amyl. Arayl is a radical analogous to ethyl and 

 methyl, the hydrated oxide of amyl being known as fusel oil, as 

 the hydrated oxide of ethyl is known as ethylic or common alco- 

 hol, and the hydrated oxide of methyl is known as methylic alco- 

 hol. Fusel oil is known to be a common impurity in ordinary 

 alcohol, and its presence in collodion has long been regarded as 

 injurious, and conducive to fog, without any knowledge of the 

 reason why it should produce mischief. Prof. TyndalTs experi- 

 ments suggest a series of possibilities. When fusel oil is in collo- 

 dion, and comes in contact with nitric acid, either free in the bath, 

 or liberated by action of free iodine in the collodion, a trace of 

 nitrate of amyl may be formed, and this body, being present in 

 the film when exposed to the action of light, and possibly decom- 

 posed, would, under some circumstances, yield, as a product of 

 decomposition, valerianic acid, a substance answering to acetic 

 acid, as the product of the oxidation of common alcohol, or formic 

 acid in methylic alcohol. Or, possibly, in the decomposition, in- 

 termediate bodies, analogous to acetone or aldehyde, might be 

 formed, with a well-known tendency^ to produce fog when present 

 in a collodion film. Such a series of possibilities exist, and might 

 furnish a clue to the fogging action of fusel oil when present in 

 collodion, which, arguing from ordinary analogies, ought not to 

 be more inimical to success than the ordinary alcohol employed ia 

 the manufacture of collodion. — Photographic News. 



PORTRAIT FIGURES WITH NATURAL LANDSCAPES. 



** I observe that considerable interest has been of late excited by 

 some prints in which portrait figures have been combined with 

 well-executed landscapes, with a perfect union of the full form. 

 The following idea may or may not be that employed by the 

 maker of the prints in question ; but it would, I think, undoubtedly 

 yield better results than the methods commonly in use, and, in 

 some respects at least, with less labor. I give it for what it may 

 be worth, not having had leisure to make any experiments my- 

 self: — 



** Provide some pieces of glass and of mica of exactly the same 

 size as the glass. Pose the model, supposed to be a standing lig- 



