A Yorkshire Rector of the Ei'^htccnth Century. ig 



rectory, likewise brought to Leeds, only a few miles from 

 Thornhill, the eminent Joseph Priestley, whose reputation 

 as a dissenting minister, and also as a man of science, had 

 already made him widely known. He had been elected the 

 year before into the Royal Society, and this year lie published 

 his History and Present State of Electricity. It was natural 

 that two philosophers, having so many interests in common and 

 living so near each other, should soon become acquainted. 

 Michell was too generous and liberal-minded to allow the 

 popular prejudice against the unorthodox clergyman at Leeds 

 to stand in the way of their friendly intercourse in science. 

 During the next five years, they saw much of each other, 

 besides carrying on an active correspondence on scientific 

 questions. Priestley has put on record that at this time he 

 frequently visited the rector of Thornhill, and ' was very happy 

 in his societ3^' In 1772, he published his two quarto volumes 

 on the History and Present State of Discoveries relating to Vision, 

 Light and Colottrs, in the preparation of which he freely 

 acknowledges how much he owed to Michell's assistance. 

 The information which he affords regarding this assistance, 

 throws interesting light upon Michell's views on a number of 

 physical problems which he had considered, but on which he 

 had never published anything. The intercourse of these two 

 philosophers furnishes another example of Michell's habitual 

 generosity and helpfulness in the cause of science. 



Priestley appears to have been impressed by the skill 

 shown by the rector in devising and constructing apparatus 

 for the purpose of illustrating or solving physical problems. In 

 particular, he alludes to an endeavour made by his friend to 

 ascertain experimentally, the momentum of light in a more 

 accurate manner than had previously been proposed. The 

 apparatus, which he describes, was disordered by the experiment, 

 but the attempt of its designer, Priestley remarks, ' was not 

 wholly without success, and the conclusions that may be drawn 

 from it are curious and important.'* He then shows that 

 these conclusions which Michell was disposed to draw, pointed 

 to the ' mutual penetrability of matter.' The account of these 

 inferences had best be given in Priestley's own words : ' The 

 ingenious hypothesis of Boscovich on this subject, or at least 

 one that is the same in everything essential, also occurred to 

 my friend, Mr. Michell, in a very early period of his life, without 

 his having had any communication with M. Boscovich, or 

 even knowing that there was such a person. These two 

 philosophers had even hit upon the same instances, to confirm 

 and illustrate their hypothesis, especially those relating to 

 contact, light and colours. 



* Discoveries in Vision, Light and Colours, p. 357 

 1918 Jan. 1. 



