i88i.J 
Analyses of Books, 
557 
his own. The latest results of Mr. Norman Lockyer in solar 
and stellar spectroscopy are stated and discussed. As regards 
absorption-spectra the author reminds his readers how these are 
affected by the solvent used, by the degree of concentration, 
and even by the presence of other bodies, and consequently 
what great care is needed in employing the spectroscope in 
analysis. 
The article on Light summarises much new and valuable 
matter, especially as regards circular polarisation. The chemical 
action of light, especially upon organic matter, — e.g., chloro- 
phyll, — is very far from being fully understood. Thus Pfeffer 
finds that the decomposition of carbonic acid by plants is most 
active in the yellow, and descends regularly on either hand from 
that point. On the other hand, Timinaseff observed the maxi- 
mum decomposition in the red, corresponding with the character- 
istic absorption-band of chlorophyll. The blue and violet rays, 
though absorbed by chlorophyll, are found to have no effect upon 
the absorptive power of plants. 
The article on Volcanic Products is exceedingly interesting. 
It appears that of the fifteen non-metallic elements twelve, and 
of the fifty-one metals nineteen, have been found in volcanic 
products. It is exceedingly probable that others will be detected 
on careful examination. We can, e.g., scarcely imagine nickel 
to be generally absent where cobalt is present. Seeing that 
iodides have been detected, bromides, as the author remarks, 
will scarcely be absent. The complexity of some volcanic 
minerals is remarkable. Thus a spongy and crystalline mass 
from the crater of the island Vulcano contained arsenious and 
selenium sulphides, boric acid, ammonium chloride, lithium 
sulphate, and the alums of thallium, caesium, rubidium, and 
potassium. 
Besides the above-mentioned, and not a few other extensive 
articles, the work contains notices of numbers of minerals, 
organic principles, and artificial products, which have either been 
recently discovered or more thoroughly examined since the ap- 
pearance of the last Supplement. 
We are not aware of any work of reference in any language, 
covering the whole extent of chemical and chemico-physical 
science, which can be placed on a level with Mr. Watts’s 
“ Dictionary.” 
