398 Transactions. — Astronomy. 



Let us think of the stream of hydrogen, oxygen, marsh gas, etc., 

 arriving near the sun at its poles ; the rise of temperature will 

 evidently bring about combustion, with its accompanying great 

 development of heat. The result of the combustion, the aqueous 

 vapour and the carbon dioxide, will flow to the solar equator, 

 and be projected into space. Thus it would appear that the 

 constitution of the interplanetary atmosphere would be gradually 

 altered ; but Sir W. Siemens here steps in with the suggestion that 

 the solar radiation would bring back the combined materials to 

 their original condition of separation, thus enabling them again 

 to flow towards the sun, and by their second combustion supply 

 the central power with further energy. It remains to show how 

 this could take place. 



There is no fact better known to students of chemistry than 

 the decomposition of substances by heat. Nearly all organic 

 substances and many metallic salts are resolved into simple 

 compounds by exposure to heat, while such stable bodies as the 

 metallic oxides, and even water itself, are broken up at a high 

 temperature. The explanation of this very general phenomenon 

 is as follows : — The substances are made up of particles, which 

 are all exactly alike, and all complex, being themselves formed 

 by an aggregation of atoms. These atoms, within the particle or 

 molecule, are subject to definite periodical motions or vibrations, 

 which increase in amplitude with the temperature. It is there- 

 fore evident that, as the motions of the atoms within the mole- 

 cule gradually increase in violence, the time must arrive when 

 the cohesive forces which hold them together must be overcome, 

 and the atoms flying off in different directions will either remain 

 at large, or will come into contact with others derived from other 

 particles, forming, in the majority of cases, simpler aggregations. 

 The destruction of the particles is, in fact, not unlike that of a 

 fly-wheel which is rotated more and more rapidly, until at length 

 the centrifugal force overcomes the cohesion of the iron, and the 

 wheel flies to pieces. 



Now, it has been shown by Tyndall and others, that vapour 

 of water and other gaseous compounds possess a remarkable 

 power of absorbing the vibrations of radiant heat, the violence 

 of the atomic vibrations becoming thereby greatly augmented. 

 Nevertheless, under ordinary circumstances, no decomposition 

 is apparent. At low pressures, however, the decomposition is 

 greatly increased, and it is reasonable to suppose that, at the 

 extremely low pressure which reigns in the interplanetary 

 spaces, the destruction of the molecules would be consider- 

 able. 



Here, then, we have an hypothesis which explains how the 

 solar radiant energy is not lost, but gathered up by the particles 

 of matter distributed in space, to be poured again into the sun 

 by the great gaseous current which circulates among the planets. 



