258 Dr. Schuster 071 



by Stewart's death. He felt the necessity not only of 

 making observations, but also of reducing and discussing 

 them. In a complicated subject like this, any discussion 

 must be founded on some preliminary hypothesis which 

 commends itself to the author's mind. Some writers in 

 publishing their result, prefer to give only what they con- 

 sider strictly proved, and to keep back the hypothesis which 

 has served them as a stepping stone. But it is doubtful 

 whether the method followed, for instance, by Faraday, in 

 which the scientific public is taken into the author's con- 

 fidence, and in which the author's train of thought is made 

 clear, is not of greater ultimate advantage to science. It 

 must always depend on the personal temperament of the 

 author which of these methods he adopts, and Stewart 

 preferred always to put forward what he called his "working 

 hypothesis." His ideas on the nature of the forces w^hich 

 produce magnetic disturbances have changed but little from 

 the year 1 861 to the time of his death. The earth itself 

 and earth currents only acted, in his opinion, in a secondary 

 way, while the primary current producing the disturbance 

 takes place in the upper regions of the atmosphere. He 

 concludes his first paper on the subject {Proc. Roy. Soc. XI.) 

 by putting forward the hypothesis that earth currents and 

 auroras are due " to the fluctuating nature of this primary 

 current " (by induction), while " the magnetic disturbances 

 are due to its absolute intensity." The various facts which 

 have come to light since 1862 have not materially altered 

 in his opinion, except in so far that in his later writings he 

 seems to ascribe a greater importance to earth currents in 

 producing magnetic disturbances. In connexion with Mr. 

 Sidgreaves, Stewart compared the simultaneous changes of 

 declination during disturbances at Kew and Stonyhurst, and 

 came to the conclusion that the ratio between the magni- 

 tudes of such changes was not constant, but depended to 

 some extent upon the abruptness of the disturbance. The 



