120 
NATURE 
_ [OcTOBER 12, 1916) 
of the petals. The results are complicated, and not 
readily summarised, but they confirm a generalisation 
already established by work in hybridisation among 
both plants and animals; that ‘views on the presence 
and action of factors obtained by an investigation of 
one single crossing are liable to modification when one 
of the forms investigated is crossed with a third form. 
Hence it is necessary to cross the same form with more 
than one partner in order to arrive, step by step, at 
the truth.” 
MATHEMATICS AND. PHYSICS AT THE 
BRITISH ASSOCIATION. 
“THE first of the two organised discussions arranged 
for this section was on ‘Gravitation."’ ‘1he 
discussion followed immediately after Prof. White- 
head’s presidential address, and it happened that the 
arrangement was appropriate, for the president’s ex- 
position of the logical texture of geometry had carried 
us far from the ordinary conceptions of space, and 
paved the way for the revolutionary ideas associated 
with the space-time world of Einstein and Minkowski. 
Mr. E. Cunningham, who opened the discussion, and 
Prof. A. S. Eddington, who followed, dealt with 
Hinstein’s recent work, which brings gravitation 
within the scope of the principle. of relativity. If an 
observer is in a closed lift, it is well understood that 
an acceleration of the lift upwards is exactly equiva- 
lent to an increase of the force of gravity, so far as 
mechanical phenomena inside the lift are concerned. 
There would, however, be minute differences in the 
optical phenomena according to the ordinary theory ; 
relatively to the accelerated lift the path of a ray of 
light would seem to be curved, whereas for the 
stationary lift it would be straight if the increased. 
gravitational field makes no difference. Accordingly, 
the first suggestion towards a relativity theory which 
shall include gravitation is that the path of a ray of 
light must be bent by the gravitational field, just as 
it is apparently bent by an acceleration of the frame- 
work of reference. The curvature to be expected is 
extremely small—amounting to a change of direction 
of 1-7” in the case of a star seen close to the sun’s 
limb—and it has not been possible to prove or disprove 
the hypothesis directly. Meanwhile the theory has 
been elaborated and generalised by Einstein, who has 
at length been able to throw the laws of motion, of 
electrodynamics, and of gravitation into a form which 
makes the sequence of phenomena entirely independent 
of any particular framework of reference. The result 
has been to yield a very striking confirmation of the 
theory, for it is found to predict a motion of the 
perihelion of Mercury amounting to 43” per century— 
just the amount of the hitherto unexplained discord- 
ance. The new theory removes what is probably the 
most celebrated of the few cases of failure of gravita- 
tional astronomy. The discussion afterwards turned 
to the experimental side. Dr. P. E. Shaw gave an 
account of his experiments which appear to indicate 
a change in the constant of gravitation with tem- 
perature, and Prof. R. A. Sampson urged that astro- 
nomical evidence is not capable of denying this possi- 
bility. Dr. W. G. Duffield read a report of the Com- 
mittee on the Determination of Gravity at Sea, con- 
sidering especially the difficulties attending the use of 
the aneroid method, and the possibility of improve- 
ments in future attempts. : 
A paper by Sir Ernest Rutherford on the ‘X-Ray 
Spectra of the Elements” was of special interest. He 
referred particularly to the researches of Siegbahn and 
Friman, who have extended the work. of Moseley to 
the elements of high atomic weight from gold to 
uranium by examining the L spectra. It appears 
NO. 2450, VOL. 98] 
that there are ninety-two elements up to uranium,. 
By finding the atomic number of lead it has now 
been possible to assign the whole series of radio-active 
products to their places. in the scheme. Sir E, Ruther- 
ford further described the work done in America with’ 
the Coolidge tube, which provides a steady high 
voltage. It is found that the maximum frequency of 
the rays which can be obtained follows closely the 
quantum relation Ve=hv, the accuracy between 
20,000 and 100,000 volts being one per cent. To 
excite the characteristic radiation of a substance a 
rather higher voltage is needed than that given by the 
quantum relation, as though it were necessary to. 
expend some energy in disturbing an oscillator. 
Prof. H. H. Turner read'a paper on the ‘* Measure- 
ment of Time,” dealing with daylight saving and 
justifying the innovation from a scientific point of 
view. ‘The paper elicited an interesting speech from 
Prof. J. Perry, who admitted that he had formerly 
rather thoughtlessly opposed the scheme, and urged 
the warning against being led by authority in science. 
Other members, however, professed themselves still 
unconverted, 
Prof. T, H. Havelock gave a review of recent work 
on the ‘‘ Propagation of a Signal in a Dispersive 
Medium.’’ He described the approximate methods of 
calculation which have been used, showing the rela- 
tion between the recent methods of contour integration 
and the older work of Hamilton and Kelvin. The 
precise nature of the “ forerunner,’’ or minute disturb- 
ance which travels through the medium in advance 
of the main signal, is a matter of special difficulty, and 
an exact solution for any particular cases that may 
prove tractable would be a great help towards progress. 
The absence of several speakers who had been ex- 
pected to take part rather detracted from a discussion 
on ‘Osmotic Pressure,’ opened by Prof. A. W. Porter. 
There were many other interesting papers, most of 
which we must pass unnoticed for want of space, but 
special mention may be made of Prof. J. C. McLen- 
nan’s paper on ‘‘Tonisation Potential,” continuing and 
extending the results communicated last year; also of 
Sir F. W. Dyson’s ‘‘Mean Parallaxes of Stars of 
Different Magnitudes,”’ which in the main confirm the 
well-known formulz given by Kapteyn in 1901. At a 
separate meeting of the department of mathematics 
Prof. G. N. Watson gave a general survey of the 
recent developments of the theory of asymptotic series. 
A: new departure, which it is hoped may lead to 
important results, was the formation of a committee 
representing Sections A and E to consider the needs 
of geodetic research. This arose from the presenta- 
tion of a report by Col. Close, Sir F. W. Dyson, and 
Col. Hills, prepared at the request of the Organising 
Committee of Section A. The report brought out 
clearly the lack of organisation and general neglect of 
higher geodesy in this country, and there was a unani- 
mous feeling that steps should be taken towards the 
constitution of some committee or association respon- 
sible for stimulating this branch of science. 
THE BRITISH ASSOCIATION AT 
NEWCASTLE. 
SECTION D. 
ZOOLOGY, 
ABSTRACT OF THE OPENING ADDRESS By Pror. E. W. 
MacBripe, M.A., D.Se., F.R.S., PRESIDENT OF 
THE SECTION. 
Tue decision of the Organising Committee to devote 
the sittings of the section chiefly to the economic and 
medical applications of zoology must not divert us 
from the task of research into fundamental laws: The 
laws of heredity had been intensively studied for the 
