174 Molecules, Ultimates, Atoms, dnd Waves, [April, 



explanation of this phenomenon is an imperfection in the 

 vapourisation. Minute incandescent solid or liquid particles 

 may be carried up in intermixture with the vapour, and give 

 rise to a weak continuous spectrum. At least it would not 

 be easy to find any other more feasible explanation. 



Confining attention to the definite bright lines, and assum- 

 ing these to be due to the vibration of the atoms constituting 

 the chemical ultimates of the gas or vapour, it is plain that 

 these atoms, while very close to each other within the limits 

 of the ultimate, cannot be in absolute contact, otherwise 

 they would be incapable of separate individual vibration. 

 They must be held together by a very powerful atomic 

 attraction ; but they must be simultaneously kept apart by 

 a correspondingly powerful elastic or repulsive force which 

 prevents their passing into absolute contact. This elasticity 

 can be no other than that of the luminiferous ether, which, 

 probably in a compressed state, must intervene between the 

 atoms and keep them asunder, balancing the atomic force 

 at a certain minute distance. 



The nearest analogy to such a condition is that furnished 

 by the extreme points of two similarly magnetised fine 

 sewing needles. Suppose the points to be both north poles, 

 and one of the needles to be fixed in an upright position 

 with its point uppermost, while the other is suspended over 

 it with its point downwards. In the absence of the magnetism, 

 the suspended needle would, by the force of gravity acting 

 alone, be attracted into a position exactly over the other, so 

 that the two needles would form a straight vertical line. 

 But the magnetic repulsion subsisting between the two points 

 will prevent their assuming this position. The upper needle 

 will become slightly inclined to the other, the two points 

 being maintained at a certain distance apart, depending on 

 the strength of the magnetism. In this case, the magnetic 

 repulsion acts the part of the elastic ether, while the 

 terrestrial gravitation performs the office of the atomic 

 attraction in the other case. But the atomic attraction 

 must in its intensity approach very nearly to that of the re- 

 pulsion exerted by the ether, so that the two forces may 

 balance each other. Were the repulsion exerted by the 

 ether much in excess of the mutual attraction of the atoms, 

 these could not approach so near one to another as they do. 

 Were the attraction in excess of the repulsion, the latter 

 could not prevent the atoms from passing into absolute 

 mutual contact. 



If such be the constitution of the chemical ultimates, it 

 may not be improbable that, in those cases in which the 



