Marcu 28, 1912| 
for Matematik on 
Lexis. 
the theorems of Poisson and 
AccorpING to an article reprinted from the Pro- 
ceedings of the Academy of Science of Amsterdam, 
Prof. Zeeman, in the course of some experiments on 
the double refraction produced in liquid air by an 
electric field, has found that liquid air will stand an 
electric field of 90,000 volts per centimetre. In his 
double refraction measurements a difference of poten- 
tial of 17,000 volts was maintained between the plates 
of a condenser 4:5 centimetres long, 1-0 centimetre 
wide, and 03 centimetre apart immersed in liquid 
air, and a beam of plane polarised homogeneous light 
traversed the liquid air between the plates. The 
phase difference introduced by the double refraction 
due to the electric field was estimated at 1/300 wave- 
length, so that the Kerr constant for liquid air is 
about 1/20 of that of carbon bisulphide. 
Tue therapeutic action of certain mineral springs 
has been recently attributed, at least in part, to the 
presence of the radium emanation in the water. Ex- 
perimental evidence in support of this view is given 
by P. Mesernitsky in the current number of the 
Comptes rendus of the Paris Academy of Sciences. 
It was found that the radium emanation decomposes 
sodium urate, some ammonium salts being formed. 
The exact nature of the decomposition (which was 
shown to be due to the action of the « rays, the 
penetrating rays being without effect) has not been 
completely made out, but there is a marked increase 
of solubility of the urate. It is suggested by the 
author that this action of the @ rays upon sodium 
monourate may furnish an explanation of the thera- 
peutic effects of the emanation in gouty cases. 
A paper by Mr. Andrea Naccari in vol. xlvii. of 
the Atti of the Academy of Sciences of Turin 
(December, 1911) takes as its starting point an old 
memoir by Samuel Hunter Christie in the Phil. 
Trans. for 1826, entitled “‘On Magnetic Influence in 
the Solar Rays.” 
oscillation of a magnet to decrease more rapidly than 
usual when sunlight fell on the magnet. The pheno- 
menon had since been studied by Baumgartner, who 
found that it was not confined to magnets, and con- 
cluded that the real cause was air currents set up by 
the heating. Naccari confirms the view that 
magnetism has nothing to do with the phenomenon, 
but he differs from Baumgartner as to the cause. 
He ascribes it to the effect of radiation on the air 
which is carried by the oscillating body and that 
immediately surrounding it. Under certain condi- 
tions, the effect of thermal radiation on the damp- 
ing seems very large, and further study of the 
phenomenon from the point of view of the kinetic 
theory of gases might not unlikely prove profitable. 
IN a paper read at the Concrete Institute on 
March 14, Mr. Reginald Ryves treated the question 
of high dams of great length, and proposed a form 
of thrust buttress dam of arches, in which the whole 
of the water load is taken by masonry in direct com- 
pression, and neither the weight of the buttress nor 
the weight of the arch is taken into account as 
NO. 2213, VOL. 89] 
re- 
Christie found the amplitude of | 
NATURE 
93 
| gards stability, except for resistance to sliding bodily 
when the ground is comparatively soft. Under 
| normal conditions, the best slope for the water face 
cone, but even then the maximum 
is 45°. The dam consists of inclined arches of in- 
_ creasing thickness as the depth increases, and sloping 
\wate ase 
The abutments rest against the up-stream 
faces of the buttresses, which are built of layers all 
inclined at 45°. Every part of such a dam is sub- 
ject to the same stress, except that the top layer of 
the buttress and the upper part of the arch ring 
may have the minimum in each case for the materials 
used. The author claims that this type is suitable for 
heights up to 200 ft. with a stress of 10 tons per 
square foot, and up to 300 ft. for 16 tons per square 
foot. 
Mr. Epwarp STanrorp has published an excellent, 
well-coloured geological map of central Europe which 
will prove of great service to students of geology, and 
less directly to teachers of geography. The map is 
162 in. by 103 in., and costs 5s. 
M. J. Danne asks us to say that his laboratory at 
Gif for experiments on radio-active substances is about 
26 kilometres from Paris, and not 206 kilometres, as 
stated in last week’s NaTuRE (p. 69). 
OUR ASTRONOMICAL COLUMN. 
ASTRONOMICAL OCCURRENCES FOR APRIL: 
Aprilt. oh.om. Neptune stationary. 
1. th.om. Jupiter stationary. 
1. toh. 14m. Moon eclipsed. Visible at Green- 
wich. 
6. 8h. 32m. Jupiter in conjunction with the 
Moon. (Jupiter 5° 8’ N.). 
to. 4h. 54m. Uranus in conjunction with the 
Moon. (Uranus 4° 46’ N.). 
10. 19h. om. 
15. oh. om. 
Neptune at quadrature to the Sun. 
Mercury in inferior conjunction with 
the Sun. 
15. 5h. 17m. Venus in conjunction with the 
Moon. (Venus o 5’ N.). 
16, 22h. 51m. Sun eclipsed, partially visible at 
Greenwich, ends at 1.31 p.m. on April 17. 
18. 18h. 31m. Saturn in conjunction with the 
Moon. (Saturn 4° 47’ S.). 
20-22. Lyrid meteors at maximum. 
22. 3h.22m. Mars in conjunction with the Moon. 
(Mars 3° 25’ S:). 
22. 21h. 53m. Neptune in conjunction with the 
Moon. (Neptune 5° 53’ S.). 
23. rtoh.om. Uranus at quadrature to the Sun. 
27. Ith. 53m. Mercury in conjunction with Venus. 
(Mercury 0° 10’ N.). 
Tue Ecuipse oF Aprit 17.—In the Revue générale 
des Sciences, the Abbé Moreux publishes an interest- 
ing summary concerning the chances of a total eclipse 
of the sun being observed on April 17 next. He 
points out that M. Landerer’s very slight modifica- 
tions of the data produced considerable changes in 
the figures showing the size and path of the shadow 
breadth of the 
latter was only 200 metres (about one-eighth mile). 
Adopting the new figures given by Dr. Crommelin, 
| the Abbé Moreux finds that totality will last 1-6s. just 
| before reaching the Portuguese coast, 1-5s. between 
Penafiel, about twenty miles east from Oporto, and 
Cavez, and about as the shadow leaves the 
northern shore of the Peninsula. He calculates that 
at St. Germain and Namur the height of the apex of 
Is. 
