TRANSACTIONS OF SECTION A. 293 
Port Darwin, in one case, and westward through Canada and the Pacific Ocean 
to Southport (Queensland) in the other case. 
It was also shown that the connection between these two meridians obtained 
by means of the measured longitudinal arcs Port Darwin-Melbourne, Melbourne- 
Sydney, and Sydney-Southport (Queensland) completes a whole longitude circuit 
round the Earth, with a closing error of less than a hundred feet. 
The reality of such a small error was questioned, chiefly on the ground that 
larger discrepancies were found in the independent results of certain links which 
have been measured more than once. 
It was pointed out that in order to render the whole of this important longi- 
tude circuit homogeneous and reliable a re-measurement should be made of the 
arcs Madras-Singapore, Singapore-Port Darwin, and Port Darwin-Southport 
(Queensland), adopting the highest refinements of modern practice and present 
instrumental means. 
The object of the paper was to enlist the sympathy of the British Association 
in this matter, and to obtain its advice as to the most practical and efficient plan 
of carrying out the work. 
TUESDAY, AUGUST 18. 
Joint Meeting with Section B (Chemistry). 
Discussion on the Structure of Atoms und Molecules. 
Sir Ernest RuruerrorD (abstract of remarks): In recent times there has 
been an accumulation of convincing evidence of the independent existence of 
the chemical atom. The atomic theory is no longer merely an hypothesis intro- 
duced to explain the laws of chemical combination; we are able to detect and 
count the individual atoms. We can determine the actual mass of an atom in 
various ways, and know its value with considerable accuracy. The idea that the 
atom is an electrical structure received a great impetus by the detection of the 
electron by J. J. Thomson; and, moreover, the Zeeman effect showed that all 
atoms must contain electrons. The atomic character of negative electricity is 
well established; we always find the negative electron, however produced, 
carrying a definite charge. We have, unfortunately, not the same certainty 
with regard to the behaviour of positive electricity, for it cannot be obtained 
except associated with a mass comparable with that of a hydrogen atom. In 
J. J. Thomson’s model of the atom the positive electricity was supposed 
(for mathematical reasons) to be distributed throughout a large sphere with the 
negative corpuscles moving inside it. This hypothesis has played a useful part 
in indicating possible lines of advance; but it does not fit in with more recent 
discoveries, which point to a concentrated positive nucleus. 
We have now two powerful methods that aid us in determining the inner 
structure of the atom—the scattering of high-speed particles in transit through 
matter, and the vibrations of the interior parts of the atom. In C. T. R. 
Wilson’s photographs of the tracks of the a particles through a gas we notice 
many sudden bends in the paths. In order to account for these deflections I 
have found it necessary to believe that there is a concentrated nucleus in the 
atom (having a certain number of units of charge), in which the main part of 
the mass resides; outside this there are a corresponding number of electrons. 
The whole dimensions of the nucleus are very small indeed compared with the 
distance of the outer electrons. From the scattering experiments it appears 
that the law of force right up to the nucleus is the inverse square law; no 
other formula would give accordance with the observations. The radius of the 
nucleus is of the order 10-'* cm. in the case of gold, and for a lighter element 
it is smaller still. The approach of the a particle to the nucleus of the hydrogen 
atom when the latter is set into very swift motion is exceedingly close—a 
distance even less than the diameter of an electron. From _ this it is 
probable that the hydrogen nucleus is simply the positive electron with a large 
electrical mass due to the great concentration of the positive charge. Another 
