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NOTICES OF NEW BOOKS. 
associated with him, both in the experimental work and in the task of 
collecting such a mass of detailed records, extending over more than a 
couple of decades. 
Sir George Beilby has made many branches of science his debtor : 
physics, metallography, microscopy, chemistry and geology, all sharing 
in the advance which has been made. 
We are concerned more particularly with the first three. Research 
such as this book describes should go far to effect a closer union between 
physics and microscopy on the one hand, and the elucidation of the 
physical meaning of metallographical phenomena on the other. For 
instance, the rather cryptic statement of the physicist that a solid 
possesses energy by reason of its surface, receives new and abundant 
confirmation when we are told that “ increase in the mobility of the 
molecules of a solid which is still far short of the freedom of the liquid 
state is sufficient to enable the force of surface tension to assemble the 
molecules of a thin film into new forms of aggregation.” 
The metallurgical reader will naturally turn to the section dealing 
with surface flow and the theory of polish ; in these fields he will find that 
the author has indeed gathered a goodly crop of new knowledge. The 
true nature of the processes of abrasion, grinding and polishing is laid 
bare, and the usual opinion that the last-mentioned is only a particular 
case of the second, well refuted. Before leaving the study of metals, 
some views of very great interest are given on the vexed subject of 
hardening. Finally, the optical properties of thin films come in for 
their fair share of attention, thus carrying on the work begun by 
Faraday some seventy years ago, and published in his Bakerian Lecture 
of 1857. Throughout the book great stress is laid on the importance 
of a thorough appreciation on the part of the investigator of the possi- 
bilities and limitations of the microscope as an instrument of research, 
also the need for careful interpretation of results dependent upon 
resolving power and Numerical Aperture. 
It seems ungracious to call attention to defects in a book such as 
this, except to show how few and unimportant they are. On page 10 
there appears to be an editorial slip (and again later on) when the 
phrase “ throughout the paper ” occurs ; a remnant, no doubt, of the 
memoir in which the observations were first published. The absence of 
an index is rather a pity, for the contents arranged at the beginning of 
each section do not facilitate ready reference very much ; for a volume 
containing such a wealth of information should be in every library of 
reference. 
It only remains to add a word of commendation to the publishers in 
producing a book worthy of the subject, well printed, and beautifully 
illustrated. F. I. G. R. 
