018 
directed to some other matter. The whole question of lunar 
influence on meteorological phenomena might be settled in a 
comparatively short space of time if the civilised countries of 
the world could agree to record all observations during a few 
years according to lunar instead of solar coordinates. Other 
problems will readily suggest themselves to you, and several 
might possibly be dealt with simultaneously. 
The great reform I have in view is this :—Before you observe, 
make sure that your observations will be useful and will help to 
answer a definite question. 
I hope that, though my frankly outspoken criticisms may not 
command universal assent, you will agree that there is some 
foundation for them, and, if so, the time is obviously not well 
chosen when observational science can be separated from its 
mathematical and experimental sisters. We hope that cosmical 
physics may remain an integral portion of Section A, and, 
though we acknowledge our weaknesses, we claim to have also 
something to teach. 
I hope that our proceedings this week may show that we can 
put aside observational detail and throw some light on the great 
and important problems with which our science is concerned. 
MATHEMATICS AND PHYSICS AT THE 
BRITISH ASSOCIATION. 
ALTHOUGH the number of communications made to the 
Section at Belfast was less than at Glasgow last year, there 
was no decrease in the interest of the meetings. The inclusion 
of cosmical physics in the subjects dealt with by the department 
for astronomy materially increased the attendance at the meet- 
ings of that department. 
In the mathematical department, Miss Hardcastle described 
the ground covered by the second part of her report on the present 
state of the theory of point groups, and stated that a further 
communication would be necessary to bring the report up to 
the present time. In the absence of the author, Prof. Forsyth 
gave a short account of Mr. E. T. Whittaker’s solutions of the 
partial differential equations of mathematical physics. Mr. 
Whittaker finds that an expression of the type 
or 
| F(z + ¢x cosu + zy sin uv, w) du 
0 
isthe most general solution of the potential equation of Laplace, 
where /is an arbitrary function of the arguments 
z+axcosu + zy sin «and wz, andz= \/ — q. 
It follows that Legendre’s, Bessel’s and other well-known solu- 
tions of the equation are special forms of Mr. Whittaker’s. 
In the same way, the general solution of the equation of wave 
motion is of the type 
on 7 
| | J(xsinu cosuv+y sin wsinv + zcos wz + : zt, Vv) du dv, 
J 0/0 
where /is an arbitrary function. Mr. Whittaker points out that 
this solution may be analysed into plane waves, and therefore 
supports the conclusion arrived at by Dr. Johnstone Stoney in 
1897, that all disturbances in the ether can be resolved into 
trains of plane waves. 
In the department of physics, Lord Rayleigh brought forward 
the question of the accurate conservation of weight in chemical 
reactions. He considered the discrepancies found by experi- 
menters too large to allow the law of conservation to be 
accepted as proved, and hoped that the experiments at 
present being carried out by Landolt and Heydweiller would 
soon lead to a definite conclusion, Prof. Morton described the 
experiments he and Mr. Hawthorne had carried out on the 
motion of a detached thread of liquid in a capillary tube. He 
concludes from them that there is some force of the nature of 
an attraction between the liquid and the material of the tube, 
which must be taken into account-to explain completely the 
phenomena observed. He further detailed how he had, in 
conjunction with Mr. Vinycomb, repeated and extended the 
work of Raps on the mode of vibration of stretched strings, and 
investigated the effect of the rigidity of the support on the 
motion of the string. 
Dr. Barnes, of Montreal, on continuing his experiments on 
the critical velocity of flow of water through tubes, has found 
NO. 1720, VOL. 66] 
NATURE 
[OcToBER 16, 1902 
that the velocity varies with temperature in the way anticipated 
from the viscosity term in the expression given by Prof. Osborne 
Reynolds in his classical paper on critical velocity. By apply- 
ing inthe case of mercury the method used in determining the 
specific heat of water, he has also found that the specific heat of 
mercury decreases at a rate which itself decreases slightly with 
increase of temperature. Lord Kelvin sent a short communica- 
tion in which he suggested that the temperature of an animal 
surrounded by a saturated atmosphere hotter than itself was 
kept down by evaporation within the lungs. 
Dr. J. Larmor, in a paper on the application of the method of 
entropy to radiant energy, showed that by defining the entropy 
of a given space containing radiant energy distributed in any 
arbitrary way, as the logarithm of the probability of the exist- 
ence of that particular distribution, the law of distribution of the 
energy with wave-length, which was recently deduced by Planck 
by considering a space filled with electrical resonators, could 
equally well be established. According to it, the amount of 
energy between wave-lengths A and A + dA radiated by a perfectly 
black body at absolute temperature ¢ is proportional to 
where a is a constant. 
Mr. Petavel gave an account of the work he had done 
towards the production of a standard of light. He considered 
that the incandescent surface of a metal of the platinum group 
heated electrically furnished the best source, and proposed to fix 
the temperature of that source by the equality of the radiation 
transmitted by suitable thicknesses of two media, the absorption 
of one of which (water) increased, and of the other (black fluor- 
spar) decreased, with increase of temperature of the source. 
Dr. C. S. Myers called attention to a variation of pitch of 
Galton and other high-frequency whistles when the wind 
pressure was changed, which he had not been able to explain. 
Lord Rayleigh prefaced a description of his own experiments 
to determine whether double refraction was produced in isotropic 
transparent bodies by their motion through the ether, by an 
account of those of Michelson and Morley, The latter led to 
the conclusion that light travelled with the same velocity, 
whether the direction of transmission was coincident with, 
across or opposed to that of the motion of the body. Lord 
Rayleigh’s arrangement would have enabled a change of velocity 
of 101° of the velocity cf light to be detected, but no change 
was observed when the light was transmitted through water or 
carbon bisulphide. The experiments on solids are not yet con- 
cluded. 
Dr. Johnstone Stoney forwarded a note in which he showed 
that by substituting for Huyghen’s wave surface, a wave film of 
finite thickness, within which the phases of the disturbances 
were given proper values, the disturbance propagated to a point 
outside the wave surface could be accurately calculated. Ina 
second note, Dr. Stoney showed how his method of resolving the 
light traversing any isotropic medium into trains of plane waves 
might be applied to explain several optical phenomena which 
have not hitherto yielded to other methods. 
Prof. E. Wilson described his experiments on the use of a 
magnetic detector in space telegraphy. His detector consists of 
an iron ring magnetised to instability by a current through a 
coil wound on the ring. The electric waves falling on the ring 
slightly disturb its magnetic state, and the disturbance is in- 
dicated by the sound produced in a telephone in series with a 
second coil wound on the ring. He finds such a detector very 
convenient and satisfactory in working. 
Prof. Minchin has found that a coherer consisting of a carbon 
rod lightly supported in aluminium stirrups in an evacuated 
glass tube decoheres better than any other form he has tried, 
and is now engaged in applying the arrangement to long-distance 
transmission. 
Dr. Marchant showed that the graphical method of determin- 
ing the discharge of a condenser through a variable inductance 
gave results which agreed very closely with the calculated dis- 
charge in those cases in which the calculation could be carried 
out. 
Mr. Butler-Burke gave a short account of his work on the 
phosphorescence produced in partially exhausted tubes by the 
passage of an alternating current round them. He concludes 
that itis due to the formation of groups consisting of a large 
| number of molecules of gas within the tube. 
