270 
Notices of Books . [April, 
to theory, for there are sufficient technical instructions for all 
the best known wet and dry processes to enable anyone pos- 
sessing the book to become an accomplished landscape photo- 
grapher. The history of photography — from the days when 
Scheele first saw lima cornua blackening in the sun, to the 
latest improvements in photo-engraving processes — is succinctly 
given in the first chapter; after which the author gives a series 
of experiments on light, which form an admirable introduction 
to his third chapter, which treats of the theory of sensitive 
compounds. This chapter is undoubtedly a tough one, but it 
will fully repay any amateur or professional for the time and 
trouble which he may take in mastering it. The next two chap- 
ters — on “ The Action of Light on Various Compounds,” and 
on “ The Support and Substratum ” — may be looked upon as a 
continuation of the third. We are now introduced to the more 
practical part of the subject, the daguerreotype being the first 
process treated of. Some practical photographers may smile at 
this exhumation, but they are perhaps not aware that it was 
employed by the French astronomical expeditions which were 
sent out to observe the transit of Venus in 1874. Where minute 
measurements of the photographic image have to be made, as 
in astronomical or spectroscopic work, the advantage of having 
a rigid immovable surface to work on, instead of an unequally 
contractile film, will be readily understood ; in fact, we are sur- 
prised that so many photo-spectroscopists should still adhere to 
the wet or dry collodion process. This being the case, the 
chapter in question might have been longer. The various collo- 
dion processes are next described, the practical instructions 
being very copious. As might have been expected, they take up 
a large portion of the book. The gelatino-bromide process 
and the old-fashioned catotype, which Capt. Abney informs us is 
still practised in remote districts in India, next claim our atten- 
tion. We next come to the various printing and toning pro- 
cesses, both on glass and paper ; printing with ferric, uranic, 
and chromic salts, the various autotype processes being as fully 
described as the secrets of trade will allow. The Woodbury- 
type process is also well described. The next chapters are de- 
voted to the photo-lithographic processes of Col. de C. Scott and 
Sir Henry James, — much used by the Ordnance Department for 
the reproduction of enlarged or reduced copies of charts and 
maps. It may interest our readers to know that large numbers 
of maps reduced by a modification of this process, introduced by 
Captain Ali Bey, the chief of the Photographic Department of 
the Seraskierate, were largely and profitably used by the officers 
of the Ottoman army engaged in the late disastrous campaign. 
Photo-engraving and relief processes are next described, but of 
course practical details are wanting, so many of the operations 
connected with them being kept secret. A print from a photo- 
relief plate, by Warnerke, produced by a secret process, is given, 
