l8 .4 Yorkshire Rector of the Eif^hteenth Century. 



vStill more remarkable was the sagacit}' which led him to 

 suggest the comparatively slight depth underneath the surface 

 at which a severe earthquake might start. As what he calls 

 a ' random guess,' he supposed that the depth of the focus of 

 the Lisbon disturbance ' could not be much less than a mile, 

 or a mile and a half, and probably did not exceed three miles.' 

 At the time he wrote hardly any data existed on which to 

 base an opinion on the subject. During the last century 

 considerable attention was devoted to this section of seismology. 

 By different methods of computation the depth of origin has 

 been found to vary up to about fourteen miles. These es- 

 timates seem to indicate that earthquakes take their rise at 

 various depths, but generally, if not always, in the compara- 

 tively superficial parts of the terrestrial crust, as Michell was 

 led to suggest. 



From what has now been stated our Yorkshire rector must 

 be admitted to have been an original genius, gifted with 

 insight which placed him much in advance of his time in regard 

 to studies that would now be classed as part of geological 

 science. His modesty led him to undervalue the importance 

 of his observations and to refrain from publishing a large part 

 of them, though lie was evidently ready at any moment to 

 place them at the service of any inquirer interested in the 

 subject. He was a great geological pioneer, and assuredly 

 the most accomplished English geologist of his day. 



II. — Contributions to Physical Science. 



It was, above all, in the realm of the physical sciences 

 that John Michell accomplished his most original and brilliant 

 work. While still in residence at Queen's College, he entered 

 on the practical study of Magnetism, and when only six and 

 twenty years of age, pubhshed his treatise on Artificial Magnets. 

 This little volume, besides setting forth the method which 

 he had devised for producing these magnets, contained the 

 results of his investigation of the phenomena of magnetism. 

 He found that Magnetical attraction and repulsion are exactly 

 equal to each other and that ' the attraction and repulsion of 

 magnets decreases as the squares of the distances from the 

 respective poles increase.' This discovery, now recognised as 

 ' the basis of the mathematical theory of magnetism,'* was 

 stated by him with his characteristic modesty. He would not 

 lay it down as certain until further experiments had been 

 made, but his work as far as it had gone, made the conclusion 

 highly probable, t 



The year 1767, which saw Michell settled in his ^ orkshire 



* Whittaker, History of Theories of Aether and Electricity, p. 55. 

 t Treatise of Artificial Magnets, p. ig. 



Naturalist , 



