42 D ALTON. 



and Lady's Diaries,' two periodicals then in considerable repute. 

 While residing at Kendal, Dalton became acquainted with Mr. 

 Gough, a man who, though blind from infancy, was yet possessed 

 of high scientific attainments. With this gentleman he contracted 

 an intimate friendship, and in 1793 was invited, chiefly through 

 Mr. Gough's favourable recommendation, to join a college, estab- 

 lished in Manchester by a body of Protestant dissenters, as tutor in 

 the department of mathematics and natural philosophy. He re- 

 signed this appointment after holding it for a period of six years, 

 but continued to reside in Manchester during the whole of his sub- 

 sequent life. 



In September 1793 Dalton published his first work, entitled 

 ' Meteorological Observations and Essays,' the materials of which 

 were, however, collected, and the work entirely complete'! 1 during 

 his residence at Kendal. A second edition was printed in 1834, and 

 he continued to pay much attention to this subject until within a 

 short period of his death, by which time he had recorded upwards 

 of 200,000 meteorological observations. 



In the year 1794 Dalton became a member of the Literary and 

 Philosophical Society of Manchester, of which, during the course of 

 his life, he filled in succession all the more important offices ; in- 

 cluding that of the presidentship, which he held from the peri 

 his election in 1817, until his death in 1844. On the 31st of Octo- 

 ber, 1794, he read his first paper to this Society, entitled, 'Extraor- 

 dinary Facts relating to the Vision of Colours,' in which he gives 

 an account of a singular defect in his own vision, known by the 

 name of colour-blindness, which rendered him incapable of distin- 

 guishing certain colours, such as scarlet and green. He first became. 

 aware of this defect in his sight from the following circumstance. 

 When a boy he had gone to see a review of troops, and being sur- 

 prised to hear those around him expatiating on the gorgeous effect 

 of the military costume, he asked, " In what a soldier's coat differed 

 from the grass upon which he trod," a speech which was iv< 

 by his companions with derisive laughs and exclamations of 

 wonder.* Until Dalton had announced his own case, and described 

 the cases of more than twenty persons similarly circumstanced, this 

 peculiar form of blindness was supposed to be very rare. In the 

 annals of the above-mentioned Society, Dalton published a long 

 series of important essays, among the most remarkable of which 

 are some papers read in the year 1801, entitled, ' Kxperimental 

 Essays on the Constitution of Mixed Gases;' * On the Force of 

 Steam or Vapour and other liquids al different temperatures in a 

 vacuum and in air;' ' On Evaporation,' and 'On the Kx]iansion of 

 by Heat.' In January 1HO.'', he read to the same Society an 

 inquiry ' On the tendency of Elastic fluids to diffusion through each 

 Other/ and in October of the same year wrote an Kssay containing 

 * Memoir, by Dr. T. S. Trail, Encyclopedia Britannica. 



