104 Notices of Books. January, 
treatise will do good service in drawing the attention of English 
capitalists to a region where such vast stores of wealth have 
been hitherto lying useless. 
Elements of Physical Manipulation. By Epwarp C. PicKerRina. 
Part I. London: Macmillan and Co. 
TREATISES on chemical manipulation have been given to the 
world by Faraday and Mr. G. Williams, not to speak of the 
instructions on the subject appended to works on chemical 
analysis. But a systematic manual of physical manipulation 
has hitherto been a desideratum. The boundaries of the two 
subjects are not, indeed, very easily drawn. As the author re- 
marks, “ the object of all physical investigation is to determine 
the effects of certain natural forces, such as gravity, cohesion, 
heat, light, and electricity.” Now, among the effects of heat, 
light, and electricity, chemical changes in the bodies acted upon 
form a very important part. Thus chemical and physical mani- 
pulation must be to a certain extent identical. The chemist is 
obliged to take note of many of the physical properties of the 
substances which come under his hands, and to account for their 
physical changes. The study of prolonged light is an intimate 
part of physics, but its action upon certain organic acids, and 
upon sugars, affords the chemist valuable means for their quali- 
tative detection and quantitative determination. This, as a 
general truth, was pointed out by Comte, who shows that every 
science supplies methods, or means of research, for those suc- 
ceeding it in the scale of increasing complication. 
Mr. Pickering begins his work with an exposition of the two 
methods—the analytical and the graphical—of mathematically 
representing and examining the results of an experiment. In 
the former method each quantity is represented by a letter, and 
the conclusions are then drawn by algebraic methods and the 
calculus, The graphical method represents quantities by lines 
or distances, with a view to their geometrical treatment. The 
former method, as the author justly remarks, is the more accu- 
rate, and would be generally preferable were it not for accidental 
errors, and were every physical law capable of representation by 
a simple equation. ‘The graphic method, on the other hand, has 
the advantage of speed, and enables the accuracy of results to be 
seen at a glance. 
The author next proceeds to give instructions for physical 
measurements—the determination of time, weight, and distance. 
Of these considerations, the first and last, though playing 
hitherto no appreciable part in chemistry, are in physics of the 
highest importance. 
Under the head ‘“ general experiments,” we find valuable 
