Notices of Books . 
[October, 
560 
from all the thousands of other particles ” which have been de- 
composed. “ Surely,” he exclaims, “ it is most improbable that 
human creatures in this small planet should be able to accom- 
plish in their chambers the destruction of particles on which the 
economy of Nature out in the Universe has mainly been de- 
volved.” Here, then, is a formal admission that these elements 
are after all naturally distinguished from their compounds. 
Our chemical readers, however, will not thank us for further 
pursuing the examination of a book which is rarely tangible, 
and which formally discourages the appeal to experiment, holding 
up the early physicists of Greece as examples, and recom- 
mending us to examine faCts with the mental eye rather than 
with that of the body. Such works appear from time to time, 
written generally by men who have little practical acquaintance 
with their subject, and pass away without having contributed 
anything to the stock of human knowledge or to our means of 
research. 
A Practical Treatise on the Steam-Engine . By Arthur Rigg. 
London : E. and F. N. Spon. 1878. 
This work is exaCtly what is described by its title. Written in 
an easy style, and with an avoidance of too much technicality, 
its contents may be readily understood by the young student or 
the mechanic, to whom it appears to be addressed rather than 
to the more scientific investigator of theories, and yet its pages 
may with advantage be consulted by the latter, for it is the 
result of careful and conscientious practice based upon scientific 
reasoning and knowledge. In the commencement the different 
measurements required in the constructive dimensions of the 
steam-engine are considered, and it is shown how, for this pur- 
pose, the English units of the foot and inch are better adapted 
than the French metre. Following this, the laws which govern 
matter in its various forms and motions are investigated under 
the different headings of Velocity, Momentum, Work, Power, 
and Centrifugal Force, each of which is carefully but clearly 
explained. 
Having thus disposed of the definitions connected with the 
main subject, we are next introduced to the horizontal steam- 
engine, with which, Mr. Rigg truly says, for compactness and 
easy accessibility to all parts no other type of steam-engine can 
compare. There are, however, different classes of these engines 
made, some for sale, others for work, and it is to the latter only 
— in which the objeCt of the designer has been to apply the dis- 
coveries of Science, and practice of experience, to means for 
the most economical production of power — that the attention of 
