The rough interpretation (^t the spectral classes enclosed in 

 square brackets is my own ; Oe5 is the class of bright line spectra 

 which were not considered by Campbell. The assumption that 

 increasing velocities indicate later evolutionary stages seems to 

 be unnecessary for Kapteyn's argument which it appears would 

 be ju.st as strong, if not stronger, if the other view had been 

 adopted. Xo analogy will suit the case, but one or two rough 

 analogies may help to hx one's ideas. A piece of coal in a loco- 

 motive may be looked upon as a small mass of energy in rapid 

 motion ; when thrown into the furnace, it parts with much of its 

 energy, it is partially vaporised and emitted as smoke which soon 

 comes to rest in its medium, in this case the atmosphere. Or, 

 consider a comet with an enormcjus velocity near the Sun ; it 

 throws off a tail of vapour which vapour loses velocity, and 

 probably enough comes finally to rest in the Ether. The life of 

 a planetesimal is roughly the same — the origin of such a body is 

 unknown to us, but its existence is a fact which should not be 

 ignored. These bodies are travelling through space with veloci- 

 ties comparable with those of the G, K and M type stars. Ulti- 

 mately, under mutual coalescence, their higher atomic elements 

 resolve into the lighter elements. At first as a planetesimal the 

 mass flies through si)ace without any diminution of velocity, but 

 as the life history outlined in my address progresses, light-wave 

 or radiation pressure commences and some of the energy is com- 

 municated to the Ether; in this way velocity is lost, and finally 

 matter in the last stage of exhaustion and approximating to the 

 Ether itself, merges its velocity in that of the Ether which is nil. 

 When the velocity of particles emitted from atoms are comparable 

 with the velocity of light, the etheric resistance becomes very 

 large. Tt is, perhaps, axiomatic to assert that no particle can 

 travel quicker than light, but this being assumed, the resistance 

 in such a case would be infinite. The case of the brilliant double- 

 star a Crux has already been adverterl to. It is composed of stars 

 of magnitudes 1.58 and 2.09, spectral class Bi, but it shows no 

 motion due to gravitation since the fir.st measures' made some S6 

 years ago. Had it been a sun-type star, the two bodies would be 

 revolving around their mutual centre of gravity in some 25 

 to 30 years. It is certain that there is no such motion, so that we 

 are^ faced with two alternatives : ( i ) that these stars, in spite of 

 their brillianc}'. are of very small mass compared with the Sun ; 

 (2) that the material they are composed of has little or no gravi- 

 tative power, or that the gravitative power is neutralised by 

 radiation pressure. 



