182 The Nebular Hypothesis : Its Present Condition. 



circumstances producing tlie increased lieat of such seasons must 

 give rise to important investigations. Thus we should come to 

 look upon the nearness of aj^proach of a comet in perihelion, as 

 an essential element in such a discussion, and perhaps also the 

 material composition of the comet itself. It has been suggested, 

 with nnich show of reason, that the larger and nearer planets 

 when in perihelion simultaneously have a considerable effect upon the 

 solar surface, by producing spots, etc., and these again, in determin- 

 ing the amount of heat radiated from the sun ; may we not, therefore, 

 expect that the arrival in perihelion of a comet from most remote 

 regions, which, if of smaller mass, often approaches the sun much 

 more nearly than they, may also produce a marked efiect on the 

 state of the solar atmosphere? Although the 11-year period of solar 

 spot frequency is too well marked to admit of any question, there is 

 already much evidence to prove that there exist many minor disturb- 

 ances, secondary maxima and minima of solar activity, which remain 

 to be exjjlained, and which may possibly be due to the occasional and 

 irregular approaches of comets. It is certain that the solution of no 

 question can be of more service to the advancement of science than 

 that of the real practical utility of comets in the economy of the 

 universe. Speculation on this point has already been too long neglected, 

 and unless it is carried on now as far and as correctly as the state of 

 modern science allows, it is certain that it will mask some other results 

 and hinder progress. Surely none can believe that these bodies are 

 mere ignes-fatai, coming and going, without being of any service to us 

 or to other systems; and although much mystery has always hung 

 about them, and still baffles our researches, perhaps the best way of 

 attaining to the solution of it is by searching for some purpose that 

 they may subserve. Without attempting altogether to set up the 

 nebular hypothesis in as favorable a light as before, the above remarks 

 and speculations may serve to indicate the position in which it stands 

 at present, and- the broader basis on which in future the question 

 must be argued. A certain degree of unity of design seems to result 

 from these theories, which is consonant Avith the order of nature. 

 Every known body in the universe appears to have an important and 

 appropriate function to perform in the development or maintenance 

 of system like our own — a function that is constant in all conceivable 

 states of existence of those systems; and while my speculations do not 

 contradict the various theories of others, they show a tendency to 

 unite them into one consistent whole. Perhaps the most distinctive 

 feature of these remarks is, that the effects I speak of must actually 

 take place, whether or not they have the importance here attached to 



