A.— MATHEMATICAL AND PHYSICAL SCIENCES. 47 



our inability to examine this region in celestial spectra. The veil of 

 atmospheric ozone overhead cuts off the spectra of the sun and stars and 

 thus hides much of the ultraviolet, constituting a great obstacle to astro- 

 physical research. On the other side of the account we may remember 

 that it protects our persons from the harmful ultraviolet rays, and that 

 without it we might not be here to conduct research at all. It has been 

 suggested by Carlo, R. W. Wood and others that on the view that 

 atmospheric ozone is generated by the absorption of short-wave lengths 

 in the sun's spectrum, it may be absent in the Arctic during the polar night. 

 This possibility has been put to the test by Rosseland, but with negative 

 results. It is doubtful whether his station was far enough away from the 

 sunlight to make his result absolutely final. But other omens are un- 

 favourable. Thus Chalonge has found that the amount of ozone present 

 in the night (using the moon as a source) is notably more than by day ; 

 and Dobson, Harrison and Lawrence have found that when the meteoro- 

 logical conditions are such as to bring air from the Arctic, the ozone content 

 goes up, and that this is particularly marked in spring, when the Arctic 

 has been without sunlight for months. The point is, however, of great 

 interest in itself, and makes the question acute of how the ozone is 

 generated. For in view of these facts it seems hard, as Dobson has pointed 

 out, to regard it as the product of the sun's ultraviolet radiation. 



No search seems yet to have been made for ozone in the planetary 

 atmospheres. In the cases of Mars, Jupiter and Saturn at all events, the 

 problem is not at first sight specially difficult. It would not be easy to 

 establish a positive result, however, unless the atmospheres of these 

 planets possess an ozone stratum at least comparable in effective thickness 

 with the terrestrial one. 



Possibility of Unknown Elements of High Atomic Weight. 



Although we are no longer at liberty to postulate unknown light 

 elements, we are free up to the present to postulate heavier ones than 

 any known terrestrially. Jeans, as is well known, has made use of this 

 hypothesis to explain the origin of stellar energy. In common with other 

 authorities he provides it by the destruction of matter, with radiation 

 of the equivalent quantity of energy (MC^) demanded by the theory of 

 relativity. So far there seems to be fairly general agreement. The 

 difficulties arise when we come to the question of stability, and here 

 agreement is not general. Jeans considers that the source must liberate 

 energy at a rate independent of the temperature. I am not qualified, and 

 shall not attempt, to discuss this point. The object of postulating un- 

 known heavy elements is to endow them with the property of going out 

 of existence spontaneously at a rate which is independent of external 

 condition, except in so far as ionisation, which involves the removal of 

 some of the electrons from the neighbourhood of protons, tends to hinder 

 the process. 



In the known radioactive elements we have of course instances of 

 unstable forms of matter, and Jeans regards these as transitional ; but 

 it must be admitted that substances which undergo spontaneous disin- 

 tegration do not at first sight form an altogether satisfactory halfway house 

 between those which are quite stable on the one side and those which 



