30 Biographical Memoir of Sir John Leslie. 



Notwithstanding the contrai-y testimony, explicitly recorded, by 

 the founders of the English Experimental School, he denied all 

 merit and influence to the labours of the immortal delineator of 

 the Inductive Logic. He freely derided the supposed utiUty of 

 Metaphysical Science, without perceiving that his own observa- 

 tions on Causation virtually contained the important admission, 

 that Physical is indebted to Mental Philosophy for the correct 

 indication of its legitimate ends and boundaries. His writings 

 are replete with bold imaginative suppositions ; yet he laments 

 the " ascendency which the passion for hypotheses has obtained 

 in the world." * His credulity in matters of ordinary life was, 

 to say the least of it, as conspicuous as his tendency to scepti- 

 cism in science. It has been jirofoundly remarked by Mr Du- 

 gald Stewart, that " though the mathematician may be prevent- 

 ed, in his own pursuits, from going far astray, by the absurdi- 

 ties to which his errors lead him, he is seldom apt to be revolt- 

 ed by absurd conclusions in other matters.'' " Thus, even in 

 physics," he adds, " mathematicians have been led to acquiesce 

 in conclusions which appear ludicrous to men of different habits." 

 Something of this sort was observable in the mind of this dis- 

 tinguished^mathematician. He was apt, too, to indulge in un- 

 warrantable applications of mathematical reasoning to subjects 

 altogether foreign to the science ; as vvheu he finds an analogy 

 between circulating decimals and the lengthened cycles of the 

 seasons ! But when the worst has been said, it must be allow- 

 ed that genius has struck its captivating impress) over all his 

 works. Whether his bold speculations lead him to figure the 

 earth as enclosing a stupendous concavity filled M-iih light of 

 overpowering splendour ; or to predict the moons arrival at an 

 age when her " silvery beams" will become, extinct ; or to as- 

 cribe the phenomena of radiated heat to aerial pulsations ; we 

 at least perceive the workings and aspirations of a decidedly ori- 

 ginal and lofty mind. This, however, is not all. His theoreti- 

 cal notions may be thrown aside or condemned ; but his exqui- 

 site instruments, and his experimental devices, will ever attest 

 the eminent utihty no less than the originality of his labours, 

 and continue to act as helps to farther discovery. We have al- 

 ready alluded to the extent and excursiveness of his reading. 



'* See Introduction to Elements of Natural Philosophy. 



