120 
NATURE 
[APRIL 4, 1912 
surface-waves due to the friction of the displaced 
material. He concludes that the velocity with which 
the waves spread over the surface decreases as the 
period of the waves increases, from 370 kms. a 
second with a period of one second to 3°07 kms. a 
second with a period of forty seconds. 
THE last four numbers of the Bollettino of the Italian 
Seismological Society contain the notices of the earth- 
quakes recorded in Italy during the first 103 months 
of 1908. Even for so short a time the catalogue 
contains accounts of more than 500 local shocks and 
ninety-four distant earthquakes. Among the former, 
it is interesting to note the frequent recurrence of the 
names of Messina, Reggio, and other places ruined 
towards the close of the year, pointing to the gradual 
preparation for the great earthquake which was un- 
heralded by warning tremors. The eruption of Etna 
in 1908 was accompanied by a remarkable series of 
earthquakes, of which full details are given. Under 
the editorship of Dr. G. Martinelli, the catalogue has 
been recently enlarged and improved. If, however, 
to the details usually given for each earthquake, the 
approximate position of the epicentre, the maximum 
intensity of the shock, and the dimensions of the 
disturbed area could be added, the value of the 
‘notices would be greatly increased. 
Messrs. NEGRETTI AND ZAMBRA have recently devised 
a new type of instrument for recording continuously 
the direction of the wind. The record is traced on the 
chart by means of a single pen actuated by the vane. 
The pen is carried by a pivoted lever, having at one 
end a roller engaging with the cam surface of a 
spiral groove, which is attached to the spindle of the 
vane. As the vane rotates, the lever moves up or 
down and the pen records the motion on an appro- 
priately ruled chart. In order to surmount the diffi- 
culty introduced by continuous rotation in one direc- 
tion, the cam is provided at the highest point with 
a gap through which the lever falls, while at the 
lowest point a spring is brought into action by a 
secondary cam, and raises the lever. This arrange- 
ment involves duplicate points on the chart, and for 
half the compass the pen may be in one of two posi- 
tions. This is a disadvantage which will probably 
be removed in the course of time. The makers are 
to be congratulated on the ingenious manner in which 
the primary difficulty has been overcome. 
AccorpD1NG to hydrodynamical theories, wave motion 
in deep liquids is accompanied by a gradual displace- 
ment of the liquid as a whole, this displacement being 
greatest at the surface. A general investigation, 
embracing an extension of Stokes and Rayleigh’s 
theorems, is given by Prof. T. Levi Civita in the 
Atti dei Lincei, xxi., 1, for the case of waves in 
canals of any type whatever. 
Messrs. E. Leitz have sent us a large wall- 
diagram which they have issued illustrating the con- 
struction and optics of the microscope. The 
mechanical parts and lenses are drawn in section, so 
as to show their construction, and coloured lines 
depict the paths of the rays of light through the 
Ne i 5 
image. The diagram should be very useful in labora- 
tories for demonstrating to students the construction 
and optics of the instrument. A descriptive pamphlet 
is issued with it. 
BuLietin No. 53 of the University of Illinois deals 
with the inductance of compact coils of wire without 
iron cores, and is written by Prof. Brooks and his 
assistant, Mr. Turner, for the use of engineers. It 
collects together a large amount of information as 
to the dimensions and weights of bare and cotton- or 
silk-covered wire, and gives a general formula for the 
inductance of coils of almost any shape the wire of 
which is wound without considerable spaces between 
the turns. If 7 is the length of wire on the coil, R 
the outer radius, b, the length, and c the radial 
depth of the coil, the self-inductance 
X0°5 log( 100+ ms ) 
26+ 3¢ 
x 107° henries. 
The ratios of the dimensions which give the maximum 
inductance for a given length of wire are b:c:R= 
12:10:20. The inductance formula has been tested 
on nineteen coils of different shapes, the inductances 
of which were determined at the Bureau of Standards, 
and in no case was the calculated value so much as 
3 per cent. different from the observed. 
ee Tob+12¢+2R 
~ b+e4R* 10b+10c+1-4R 
AccorDING to theory, two stereoisomers of sym- 
metrical dichloroethylene should exist. Two sym- 
metrical diiodoethylenes are known, and in the 
Comptes rendus of the Paris Academy of Sciences for 
March 18, G. Chavanne describes the isolation of the 
corresponding chlorine derivatives, hitherto unknown. 
Commercial dichloroethylene was fractionated in a 
Young column of eight sections, and was separated 
into approximately equal amounts of two isomers, 
boiling at 49° C. and 60'2° C. respectively; both gave 
figures on analysis corresponding with the. constitu- 
tion C,H,Cl,. Contrary to expectation, the dibromides 
C,H.Cl1,Br, obtained from each by the action of 
bromine are identical, and further work on the space 
relations of these isomerides is in progress. 
An index to Nos. i—xvi. of the Annual of the 
British School of Athens has been compiled by Mr. 
Arthur M. Woodward. Its main purpose is to make 
more accessible the contents of the reports of the 
excavations undertaken by the school, or in connection 
with it, especially those at Knossos, Palailkastro, and 
Sparta. The index may be obtained from Messrs. 
Macmillan and Co., Ltd., and its price is ros. net. 
Messrs. Watts AND Co. have published for the 
Rationalist Press Association, Ltd., at the price of 
sixpence, a new and revised edition of Sir Ray Lan- 
kester’s ‘‘The Kingdom of Man.’ The author has 
revised ‘‘the text so far as to alter here and there 
the terms of reference to events and discoveries which 
are now six years older than they were when the 
book was first printed.” An improved figure show- 
ing the relative size of the cerebral hemispheres in 
the extinct mammal Dinoceras and large mammals. 
now living has been substituted for that previously 
optical system and the formation of the magnified ' published. 
NO. 2214, VOL. 89] 
