NOVEMBER 15, 1906| 
NATURE 51 
in these columns. The only change in the present 
edition is the incorporation of a supplement, prepared 
by the translator, giving the derivation, step by step, 
of the difficult formula in Dr. Stodola’s treatise; this 
supplement will be very acceptable to advanced 
students in our engineering schools. It is a striking 
proof of the high estimation in which this text-book 
is held in the English-speaking world that a second 
edition of the translation should so soon have been 
called for. 
(2) In their preface Messrs. Stevens and Hobart 
point out that while a number of treatises on the 
steam turbine has been published, none of them so 
far has dealt with the subject from the point of view 
of the purchaser and user, though to them the ques- 
‘tion of economy, not only in steam consumption, but 
also in first cost and maintenance, is of the greatest 
importance. In the second chapter the authors dis- 
cuss the much vexed question of units; they abandon 
the well-known B.Th.U., and adopt for their unit, 
both for heat energy and mechanical energy, the 
kilowatt hour, or K.W.H., though expressing an 
abstract preference for the kilogram-calorie as the 
unit of energy; similarly for the unit of power they 
have almost exclusively adopted the kilowatt (IX.W.) 
in preference to the older unit, the horse-power (H.P.). 
Since in dealing with the economy of steam turbines 
the authors have reduced all the results to kilograms 
of steam per kilowatt hour output from the dynamo 
driven by the turbine, it is inevitable that they should 
discard the older units. We do not think, however, 
that the well-known B.Th.U. will be displaced for 
many years to come; it is still the unit in which most 
English-speaking engineers think who have to deal 
with practical problems connected with the generation 
of steam, and it has certain practical advantages. 
That some changes in our system of units will come 
in course of time we have no doubt, and we have 
equally no doubt that they will be to the advantage 
of British and American engineers, though we cannot 
agree with the somewhat far-fetched hypothesis of 
the authors that ‘‘ the rapid rate at which Germany 
and Switzerland are coming to the front as rivals of 
English-speaking countries in manufacture and com- 
merce ’’ is due to our present system of units. 
To each of the types of turbines which have so far 
been successful on a commercial scale (De Laval, 
Parsons, Curtis, Rateau, &c.), and to several others 
still more or less in an experimental stage, a separate 
chapter is devoted. In each of these chapters the 
authors follow a definite procedure; they deal with 
the turbine, which is being considered, under two 
heads (not always in the same order) :—(a) its 
economy as a machine for the conversion of heat 
energy into mechanical energy; (b) its design from 
the point of view of the user. In the sections devoted 
to steam economy, the effect of varying the boiler, or 
admission, pressure, of varying the vacuum, and of 
superheating the steam is fully treated with the aid 
of most elaborate and carefully drawn up tables, and 
curves are plotted from these tables, both at full and 
half loads, and the thermodynamic losses are analysed ; 
in the portion of each chapter treating of design, the 
NEOs su VOL. 75)) a" * 
mechanical principles underlying the design of the 
turbine under discussion are explained with the aid 
of a number of reproductions of working drawings, 
unfortunately on such a small scale as often to render 
it impossible to make out clearly the details. 
An interesting point brought out by the elaborate 
analysis the authors have made of numerous pub- 
lished tests of De Laval and Parsons turbines is 
that while in the former a considerable reduction in 
the weight of steam per kilowatt hour is produced 
by increasing the boiler pressure, there appears to 
be but little gain in this respect in the case of the 
latter when condensing, if the pressure is increased 
beyond 8 atmospheres, assuming, of course, that the 
same vacuum is maintained in each case. It is only in 
the case of the De Laval and of the Parsons turbines 
that the results of sufficiently mumerous tests have 
been published to enable the authors to discuss fully 
all the factors which make for economy in any 
given set of conditions, but they have in all cases 
given all the information which is so far available 
for each type of turbine. 
In connection with the Rateau turbine, full details 
are given of the regenerative heat accumulators which 
have been erected at various works, where the steam 
working the turbines is the exhaust steam from 
previously existing reciprocating steam engines. In 
chapter xiii. are a series of steam tables, both in 
metric and in English units, from pressures of } lb. 
to 200 Ib. per square inch, and two other useful 
tables, one the calorific values of fuel, the other losses 
in converting the energy of 1 Ib. of coal into electrical 
energy. Two valuable chapters are xv. and xvi., 
since in these first typical results are given as to 
steam economy in modern piston engines, and then 
the authors enter into an elaborate analysis of the re- 
spective merits of the piston engine and the turbine 
from the point of view of working expenses. They 
point out that forecasting the future is by no means 
an easy matter; it is certain, however, that the 
relative positions of these two types of engines as to 
economy in steam consumption will depend to a large 
extent upon the amount to which their special 
characteristics are developed and utilised, such as the 
fact that a high vacuum is more beneficial to the 
turbine than to the piston engine from the point of 
view of economy, while, as regards superheating, 
apparently the reverse holds. 
The next five chapters deal briefly with such 
problems as the foundations and engine buildings 
for turbines, and the cost and arrangement of separate 
condensing plants, all the data collected in regard 
to each point being grouped into a series of reference 
tables. In chapter xxii., a very lengthy one, the 
authors have brought together in the form of very 
carefully arranged tables all the published details of 
some twelve of the largest and most modern steam- 
turbine plants, and in addition there are som¢ hundred 
illustrations; the many blank lines in these tables 
show how difficult it is to obtain information on points 
of great importance in connection with the planning 
of such plants. 
The final chapter is devoted to marine steam tur- 
