WATORE 
[Zune 17, 1886 
liable to earthquake are those near to active or recently 
active volcanoes, especially the Pacific border (which 
actually contains 172 out of a total of 225 now active vol- 
canoes); also earthquakes are propagated chiefly a/ong 
valleys or ridges. 
The distribution of earthquakes in time has been much 
discussed, but no periodic law either secular, seasonal, or 
diurnal, either for the werld in general or for any one 
place, is very clear. 
After discussing the synchronism of earthquakes with 
numerous physical phenomena (positions of heavenly 
bodies, states of air, &c.), the causes of earthquakes are 
considered, and the conclusion is drawn that the primary 
causes are probably terrestrial, such as (1) sudden cracks 
consequent on over-stretching of the earth’s crust during | 
| of it, the upper surface of the conductor be touched by 
elevation ; (2) explosions of steam ; (3) collapse of hollows 
produced by volcanic ejection and by the continuous 
solution and removal of matter by springs ; (4) change of 
load over large areas due to rise and fall of the tides and 
to changes in air-pressure. 
As to prediction of earthquakes, nothing certain is yet 
known. In many cases there are noticeable changes in 
springs and wells preceding earthquakes. 
warning is, however, obviously possible, viz. the report of 
an actual earthquake on one side of the Pacific could be 
at once telegraphed to the other side, thus giving twenty- 
four hours’ warning of the probable advent of a great sea- 
wave. 
As to earth-tremors, two curious cases are quoted : (1) 
the extra crowds of people in Greenwich Park on public 
One useful | 
holidays cause extra shaking in the Greenwich Observa- | 
tory instruments ; (2) certain delicate observations pro- 
jected at Cambridge in 1880-82 proved futile in con- 
sequence of the continuous earth-tremors masking the 
delicate effects sought. To these might now be added in 
London the tremors produced by the Underground Rail- 
way. Systematic record of earth-tremors (micro-seismo- 
graphy) has now been made in Italy in many towns for 
ten years: these tremors appear to be periodic, and to 
be connected with the sun’s and moon’s motions, and 
with the state of the barometer, and to increase before 
earthquakes, so that there is some hope of possibility of 
earthquake prediction from this research. 
The phenomena of earth-pulsations and -oscillations 
quoted are numerous and interesting, but space fails to 
enumerate them. 
The work begins with an earthquake-map, and ends 
with a list (10 pp.) of earthquake-literature, 
This work is well worthy of its place in the Inter- 
national Scientific Series, and may be accepted as a 
monograph on its subject by an accomplished’ seismo- 
logist, who, from his residence in Japan, has had ample 
opportunities of studying the actual phenomena. 
ALLAN CUNNINGHAM, Major, R.E. 
FRICTIONAL ELECTRICITY 
Frictional Electricity. By Thomas P. Treglohan. 
don: Longmans, Green, and Co., 1886.) 
(Lon- 
HIS is a little book written for first beginners in the 
study of electricity. On the whole it is satisfactory ; 
although the writer betrays curious want of knowledge or 
want of judgment here and there. The diagrams are 
good, and.the descriptions fairly clear ; and from place to 
place instructions are given to teachers as to experiments 
they may make before elementary classes for the purpose 
of illustrating and bringing home to the learners the 
various parts of the subject. The construction of simple 
pieces of apparatus, such as a boy may make for himself, 
is also described throughout the book and in a number 
of paragraphs at the end. 
There are, however, certain points to which we take 
serious exception. First, we cannot regard Mr. Tre- 
glohan’s mode of looking at inductive phenomena as 
correct or satisfactory. For example, speaking of the 
electrophorus, he says :—‘‘If, while the conductor rests 
upon the excited cake and is under the inductive action 
the finger, the free negative passes to the earth, and an 
equal quantity of positive enters the disk from the earth.” 
The same statement is made on the following page, so 
that there is no doubt whatever that the statement about 
the “equal quantity of positive” is really meant. In the 
diagrams throughout the book too, where discharge as 
the result of induction is going on two little arrows are 
shown, one marked + and the other —, and pointing in 
dissimilar directions. This seems to us particularising 
| with a vengeance the action of two fluids. 
On p. 35, under the heading “ specific inductive capa- 
city,” we are told that “ It was established by Prof. Fara- 
day that, for an excited body to act upon a conductor by 
induction, some substance must exist between the two 
through which the electricity may be imparted.” Shade 
of Faraday ! 
At the end of this paragraph, speaking of specific in- 
ductive capacity, we are told that “dry air is superior to 
moist air in this respect.” We do not think that any 
difference has been proved to exist between dry air and 
moist air, either as to induction or as to conduction ; 
though there is a common misapprehension (shared by 
the present author, p. 30) of a difference as to this latter 
quality. 
The use of the condensing electroscope seems to be 
misunderstood by the author. It cannot be used in 
the way described for testing “lightly charged bodies.” 
Its main use is for testing a weak but continuous 
source. 
There is also an extraordinary paragraph about a white- 
hot iron ballon p. 107, for which the author seems to make 
Prof. Guthrie responsible, and in which the experimenter 
is told to put a white-hot iron ball on the electroscope in 
order to prove certain statements! We fear the experi- 
menter will not obtain much valuable information from 
the experiment ; and it is so¢ ¢rwe that, with respect to 
the supposed indifference of a white-hot body to electri 
fication, “in this it resembles the indifference to mag- 
netism of a white-hot iron ball.” 
A few misprints we have also noticed. Sir William 
Thomson’s name should be spelled without a “ p”; iodine 
and starch paper is coloured blue, not brown, by ozone. 
Putting aside these defects, however, this little book will 
probably be found useful to teachers for the elementary 
stage in the Science and Art Department, for whose 
benefit, as we are told in the preface, it has been com- 
piled. (fnite Js 
a 
