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; including that of the presidentship, which he held from the period of his election in 1817, until his death in 1844. On the 31st of October, 1794, he read his first paper to this Society, entitled, 'Extraordinary 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 distinguishing 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 surprised 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 received by his companions with derisive laughs and exclamations of wonder.[16] 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, 'Experimental Essays on the Constitution of Mixed Gases;' 'On the Force of Steam or Vapour and other liquids at different temperatures in a vacuum and in air;' 'On Evaporation,' and 'On the Expansion of Gases by Heat.' In January 1803 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 Essay containing an outline of his speculations on the subject of the composition of bodies, in which he gave to the world for the first time a 'Table of Atomic Weights.' In the following year he communicated his views on the theory of definite proportions to Dr. Thomas Thomson, of Glasgow, who at once published an abstract of them; and in 1808 Dalton himself published the first volume of his new system of Chemical Philosophy, in which he placed the Atomic Theory on a firm and clear basis, and established the law of Multiple Proportions. The value of Dalton's researches on this great subject is immense; by the promulgation of his views Chemistry became for the first time a science, and one great law or theory was seen to govern its actions; before it was a series of separate facts, but by this fundamental law and its branches, and by this only, it is preserved as a science.