1896.] Recent Literature. 565 
body in question; but for wave-lengths which are strongly absorbed by 
the given substance, Cauchy’s formule for the intensity of metallic re- 
flection should be used.” It appears from these formule that the 
intensity of the reflected light depends on the index of refraction and 
on the coëfticient of absorption of the substance presenting the reflect- 
ing surface. Since both these factors are different for light of different 
colors, it is shown that white light must be reflected with some of its 
“ components ” relatively weaker than others, i. e., no longer in the 
proper proportion to give the sensation of white light. The application 
to the colors seen in the mineral kingdom is illustrated by the example 
of magnesium cyanplatinite, Mg Pt (CN),, where,—as is true of most 
crystals,—the index of refraction and the coéfficient of absorption vary 
with the direction in which the light vibrates, as well as with the wave- 
length of the light. The extent to which true surface color is observ- 
able on minerals is not indicated, though the possibility of a very wide 
application is clearly shown. 
In the appendices, certain mathematical aspects of the subject are 
treated in a manner suited to the requirements of physicists.—A. C. G. 
The Whence and Whither of Man.’—This book comprises a 
series of lectures dilivered at Union Theological Seminary, with some 
additional matter. The author discusses the doctrine of Evolution 
from the standpoint of a theologian. He endeavors to show that the 
great law of animal and human development as revealed in the sequence 
of physical and mental development is that those species survive which 
are best conformed to their environment; that this law holds good in 
the development of the rational, the dominant faculty in man; and 
finally, to become higher man he must develop a moral-nature by 
attaining a knowledge of himself as a moral agent, and while not dis- 
regarding the body, he must subordinate its appetites to the higher 
motives furnished by right and duty. It is in following this line of 
thought that the author hopes for a definite answer as to the future 
destiny of man. : 
The closing chapter deals with the present aspects of the theory of 
evolution, He here compares the various hypotheses of evolution and 
considers their merits. He judiciously selects the good elements of all 
of them, concluding that “ each theory contains important truth.” He 
concludes that Nägeli’s view of “ initial tendencies ” is too often under- 
valued. “My own conviction is steadily strengthening that without 
*The Whence and Whither of Man. By John M. Tyler, New York, 1896, 
Charles Scribner’s Sons, Publishers. 
