588 

sistencies met with in alternating current work. 
The only serious criticism that may be offered 
is that it attempts rather too much. For example, 
in Problem 55, on p. 275, the student is asked to 
calculate the self-induction of a long three-phase 
transmission line, and in the next question to 
calculate the corresponding reactance. He might 
be led to expect that this result would give him 
the drop of the line, whereas it does not, because 
the mutual induction between the lines and the 
difference in phase between the currents in the 
lines are not taken into account. One might also 
be inclined to criticise the amount of space 
devoted to the subject of armature windings for 
alternators. This is defended in the preface, as 
a useful mode of teaching polyphase current 
technology. In practice an oscillograph demon- 
stration of phase differences would be much more 
illuminating. The order of taking up the subject, 
too, strikes one as rather unnatural. It is surely 
a mistake to leave out any reference to the 
physical nature of self-induction and capacity until 
reactance has been studied. 
The argument from the concrete example to the 
abstract theory is much used in America and else- 
where, and possibly has advantages for engineering 
students; the danger of it is that the student, 
when he can calculate what he wants to calculate’ 
about his machines, will often never bother to find 
out the reasons for his methods; he will become 
a rule-of-thumb man instead of a scientifically 
trained engineer. The danger is a very real one, 
which must be combated if engineering students 
are to become useful in engineering development 
work, the work for which engineering colleges 
should strive to train their men. In spite of 
minor defects, the book may be recommended as 
a satisfactory text-book for students of electrical 
engineering in the early stages of their training. 

OUR BOOKSHELF. 
The. Electric Dry Pile. By C. E. Benham. 
Pp. 37. (London: P. Marshall and Co., 1915.) 
Pies Us. i ie ti 
Tuis little book is a reprint of articles published 
in the English Mechanic during the present year. 
The dry pile, built up in the same way as Volta’s 
moist pile, was the invention of Jean André De 
Luc, who first described it in Nicholson’s Journal, 
1810. It was constructed by piling up in a glass 
tube a series of paper discs, coated on one side 
with silver leaf and on the other with thin leaves 
of zinc. A continual difference of potential was 
found to exist between the terminals. Modifica- 
cations were introduced by various workers, 
NO. 2387, VOL. 95] 
NATURE 


[JuLy 29, 1915 
notably Zamboni and Singer. The latter devised 
the form of apparatus now in the Clarendon 
Laboratory of the Oxford University Museum. 
This is arranged to ring a small bell, and its 
period of activity now extends to seventy-five 
years. Mr. Benham gives detailed instructions 
for setting up a dry pile of 2000 pairs, and de- 
scribes a number of interesting experiments that 
may be carried out with its aid. The chief origi- 
nal feature is the use of two ready-made coated 
papers in the construction of the pile. The work 
would have been of greater scientific value if 
some quantitative results had been included. 
War Map of Italy and the Balkan States. 30 in. 
x 4o in. (Edinburgh: J. Bartholomew and 
Co., n.d.) 1s. net in case, or 2s. 6d. on cloth 
in case. 
THIS map covers an area extending from Geneva 
in the west to Odessa and Asia Minor in the east. 
On the north it reaches Vienna, and takes in 
Malta on the south. Insets, on large scales, of 
the Dardanelles, Constantinople and its environs, 
and Trieste and its surroundings are provided. 
Each separate State is distinguished in colour, and 
railways are shown. The map, which may be 
highly recommended, can also be obtained on | 
rollers and varnished for 6s. 
All About Zeppelins and other Enemy Aircraft. 
By F. Walker. Pp. 32. (London: Kegan 
Paul, Trench, Triibner and Co., Ltd., 1915.) 
Price 6d. net. 
Ir appears, from the preface, that “this little 
book is intended to explain fully, to a person of 
average intelligence, the nature and construction 
of enemy aircraft...” The author is a civil 
engineer, if one may so interpret the letters 
appearing after his name, but it is clear that his 
engineering training did not include an adequate 
course in aeronautics, or even freehand drawing, 
otherwise one might have been spared the many 
inaccuracies to be found in the book, and the still 
more remarkable sketches (signed ‘“‘F. W.”) pur- 
porting to represent aircraft. Fig. 20, page 25, 
is said to show ‘‘a British biplane in flight.” It 
is in reality a very poor sketch of the Wright 
biplane of 1908, to the under-carriage of which 
the artist has added a misrepresentation of four 
wheelbarrow wheels. A somewhat better sketch 
of a rear view of the same machine is introduced 
in the following words: “Several of the Allies’ 
biplanes have two propellers, as shown by the 
front view of a machine, Fig. 21.” 
Figs. 22 and 23 purport to be sketches of a 
“Taube” and an “Aviatik” respectively. Mr. 
Walker seems to have had misgivings, for he 
says: “But the details of these are so constantly 
changing, and the fact that they are utterly 
wrecked on reaching the earth, that we can only 
present the outward appearance in flight” (sic). 
It is difficult to believe that the delightful humour 
of these drawings, and of many of the statements 
in the book, is unintentional. 
