Noiwes respecting New Books. 755 
gases &c. is given. In chapter III. on the Dilatation of Solids, 
Liquids and Gases, the Editor adds the interesting observations of 
Tait on the properties of fresh and salt water at various pressures 
and temperatures. Here we are once again reminded of the 
classical experiments of Dulong and Petit and of Regnault on the 
absolute expansion of mercury, and may, perhaps, be permitted a 
brief digression as to the determination of this valuable constant 
in a less cumbersome manner. If the mercurial barometer is 
raised in temperature uniformly, the column lengthens pro- 
portionately to the diminishing density of the mercury and 
independently of the expansion of the envelope. Comparison with 
a standard barometer affords, then, the absolute expansion 
coefficient. In carrying out the experiment the vacuous extremity 
of the barometer is extended upwards or bent to one side and kept 
cool to avoid the correction for vapour-tension. The heating is 
done by a steam-jacket. The troublesome separation of the hot 
and cold mercury columns is here eliminated. 
Several additions are made under the section treating of the 
dilatation of gases, such as Witkowski’s experiments on the 
thermal expansion of air; Chappuis’ on the pressure coefficient ; 
Ramsay’s and Travers’ on the expansion and pressure coefficients 
of krypton, argon, and helium. 
In the chapter on Calorimetry we find a very full account of 
Lussana’s labours on the specific heats of gases at constant pressure 
by a modified Regnault method. ‘The reference to the important 
subject of heat of combustion might with benefit be extended. 
In this chapter the consideration of the Dynamical Equivalent finds 
a place. The section is excellent, but we think, as perhaps the 
central fact in the study of Heat, it would have been better to have 
devoted to this subject a separate chapter. The Editor adds the 
large-scale experiments of Reynolds and Moorby, Griffiths’ 
electrical experiments, as well as a short account of the work of 
Schuster and Gannon, of Callendar and Barnes, and finally a 
comparison of all. The section is further improved by a clearly 
worded discussion of the variation of the specific heat of water and 
the choice of a thermal unit. 
The chapter on Change of State is enriched by articles on the 
modern methods for the liquefaction of gases and attainment of 
low temperatures; by Griffiths’ experiments on the latent heat of 
steam, and by Lord Kelvin’s beautiful calculation of vapour- 
pressure at curved surfaces of liquids. Aitken’s experiments on 
the cloudy condensation of aqueous vapour produced by dust might 
with advantage be referred to here. We think, also, that 
M‘Connel’s very important observations on the plasticity of ice 
should be given a place in the body of the text and not be confined 
to a footnote. Erroneous references to this matter are common 
in current geological literature. 
The principal feature of Mr. Cotter’s editorial work is the 
treatment of the subjects of Radiation and Absorption. These 
sections are almost entirely his own, and we think they will be 
