564 
Notices of Books. 
[Odtober, 
water that is much needed, and greatly facilitates every process 
for the treatment of the sewage. One of the most telling argu- 
ments against irrigation, as ordinarily practised, is that in 
seasons of heavy rain, when the soil is least able to bear any 
additional quantity of water, the most is forced upon it by the 
swollen sewers. Where Mr. Latham’s plan, or any similar 
scheme, is adopted, this objection falls away. Sewage-precipi- 
tation works are also much embarrassed by floods when the 
deposit is in danger of being swept out of the tanks and carried 
into the rivers. 
The chapter on the sanitary appliances of a district, as 
affedting the quality and quantity of the sewage, contains some 
statements with which we cannot agree. That “ in the sewage 
of a midden-stead town there is a larger proportion of urine 
present in a given volume of sewage than is found in a water- 
closet town ” is simply impossible, and the “ excess of chlorine,” 
upon which so hazardous an assertion is built, is therefore no 
sure guide. 
A large proportion of the matter in this book, though of little 
interest to the general reader, is certain to be most valuable to 
the engineering profession and to municipal authorities, who 
will find it a priceless manual of reference. 
The Steam-Engine considered as a Heat-Engine. By James H. 
Cotterill, M.A., Professor of Applied Mechanics in the 
Royal Naval College. London : E. and F. N. Spon. 1878. 
This work is represented, in the Preface, as a second edition of 
some Notes on the Theory of the Steam-Engine, published in 
1871. It has, however, been so supplemented and added to as 
most considerably to enhance its value. The objedt of the 
present book is stated to be to study the process of the conver- 
sion of heat into work in steam-engines ; and the experiments 
of Regnault, Raukme, and others, are not only repeatedly veri- 
fied, but also worked out to their natural conclusions, aided by 
the further experience which has, since their days, been obtained 
on the subjedl. 
In a chapter on the physical properties of steam it is explained 
that the “total heat of evaporation of water is the quantity of 
heat requisite to raise a pound of water from 32 0 to a particular 
temperature, and evaporate it at that temperature, while the 
latent heat of evaporation of water is the quantity of heat 
requisite to evaporate a pound of water at a given temperature.” 
This latent heat diminishes as the temperature increases, ap- 
proximately by rather more than seven-tenths of a thermal unit 
for each degree of Fahrenheit ; this rate of diminution is, how- 
