358 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Mr Langmuir, adopting the Parson hypothesis, has designed an atom 
made of ring electrons round a positive nucleus in which the number 
of electrons in each shell is twice the square of the radius, giving 2 
in the first shell, 8 in the second, 18 in the third, 32 in the fourth, 
and so on, and he has also supposed the ring electrons to lie with their 
orbits in radial planes passing through the centre of the atom. It is 
evident that, in order to conceive of such an atom, we must assume a 
certain rigidity in the electron ring; and if we imagine these electron 
rings to place themselves equally spaced in a series of shells owing to 
the electrostatic attraction and repulsions, each ring will turn within 
its given shell so as to obtain the maximum number of lines of magnetic 
force passing through the ring. Such a 
radial arrangement of the rings, therefore, 
seems reasonable, as, at any rate, a first 
approximation to their position, though 
doubtless it will be modified to a certain 
' extent by the layer of rings below. If 
imagined to occupy such positions, they will 
correspond to the circle of little magnets 
which we have already considered, head to 
tail round the ring. 
In the model shown in fig. 5 the 
second shell of the Langmuir atom is 
shown, though, with a view to simplicity, 
the first shell of two electrons and the 
double number of electrons which he sup- 
posed to be contained in each cell have 
been left out. A single electron is also shown in the third shell, thus 
corresponding to a monovalent element like potassium or sodium. If the 
model is inspected, it is evident that this ring in the outer shell is in a 
stable position, having set itself with reference to the rings in the inner 
shell so as to have the maximum number of lines of force passing 
throuo^h it. 
Diagram 6 shows two models, the second model being also supposed 
to have one outer electron and these two electrons to have approached 
each other and swung into their new position. This also is in agreement 
with Mr Langmuir’s hypothesis, who showed models with the attracting 
electrons arranged in this way at the British Association Meeting in 
Edinburgh in 1921. We must suppose, then, that each of these outer 
electrons is held in its shell by the electrostatic attraction of the 
