* 



IX 



was made the Bakerian Lecture for the year 1892. In 1857 Professor 

 Thomson read a paper to the British Association, on " The Grand 

 Currents of Atmospheric Circulation." It appears that his attention 

 was first called to this subject when, during the period of his early 

 delicacy, his father asked him to look into the question of the Trade 

 Winds and write a short account of this atmospheric phenomenon 

 for a new edition of Dr. Thomson's ' Geography,' which was then in 

 preparation. This was done ; but young James Thomson found so 

 little satisfaction in the information and theories which he then 

 studied for the purpose that his mind .was keenly directed to the 

 question; and in 1857 he himself had formed a theory which he 

 expounded to the British Association. 



The subject was before his mind during the rest of his life ; and 

 though on account of other pressing work the complete publication of 

 the theory was from time to time deferred, yet it was always his in- 

 tention to return to the question. When in the last years of his life 

 the affliction of partial blindness came upon him, and when he had 

 somewhat recovered from the first depressing effects of finding him- 

 self thus sadly crippled, he set himself in his enforced leisure to 

 complete this work, and, with the assistance of his wife and daughters, 

 to produce the important paper which was read before the Hoyal 

 Society on the 10th of March, 1892. In this paper a historical 

 sketch is given of the progress of observation and theoretical research 

 into the nature and causes of the trade- winds and other great and 

 persistent currents of atmospheric circulation. Previous theories 

 are discussed and criticised and their merits duly recognized, the 

 theory of Hadley, in particular, being shown to be substantially true. 

 A much more complete theory is then expounded in full detail ; and 

 charts and diagrams in illustration show the nature of the aerial 

 motions. 



Here this memoir must close. There are many papers of Thomson 

 which have not even been alluded to iu it. Nor is it possible or 

 necessary for the present purpose to refer to all the subjects to which 

 his ever active mind directed itself. A character so truly philosophic 

 it is very rare to meet. His was a singularly well ordered and well 

 governed mind. It was, if one may venture to say so, almost too 

 philosophical and too well governed for the business of every-day 

 life. He could scarcely realise a difference between greater and 

 smaller error or untruth. Great or small error and untruth were to 

 be condemned and resisted; and, perhaps, in the matter of public 

 business and in this hurrying nineteenth century pressure, there 

 were those who, thoroughly conscientious themselves, could not yet 

 feel perfect sympathy with his extreme and scrupulous determination 

 to let nothing, however small, pass without thorough examination 

 and complete proof. To temporise was not in his nature ; and this 



