82 Biographical Account of the late JonN D ALTON. 



and tbc rudeness of tho apparatus which he employed, approached very 

 near the truth. 



In the year 1801, Mr. Dalton read a paper on the constitution of 

 mixed gases, which was published in the fifth volume of the first series 

 of the Memoirs of the Literary and Philosophical Society of Manchester. 

 According to his view of the subject, the particles of simple gases repel 

 each other with a force inversely as the distance of their centres. But 

 the particles of heterogeneous gases neither attract nor repel. The con- 

 sequences of this will be, that when heterogeneous gases are mixed, 

 they mix equally, and occupy just as much space as they did before 

 mixture. 



He explained, at the same time, that when water mixed with the atmo- 

 sphere, it assumed the form of vapour, which possessed all the properties 

 of a gas, except that by compressions and cold it was easily reduced again 

 to the state of vapour. He pointed out a very simple method of deter- 

 mining the bulk of vapour in air at all temperatures, and constructed a 

 table by means of which the volume of vapour in the atmosphere may be 

 determined at all temperatures. If we suppose that the specific gravity 

 of steam increases as the temperature, it is easy from this table to deduce 

 the weight of vapour in the atmosphere at all temperatures. 



This theory of mixed gases, which is explained by him in the third 

 volume of Nicolson's Journal, is of immense importance in meteorological 

 investigations, and constitutes, undoubtedly, one of the most important of 

 the additions which Mr. Dalton made to natural science. 



In the Annales de Chimie, for October, 1845, there is an elaborate 

 paper by Regnault on this subject. He gives, from his own experiments, 

 a table showing the elasticity of vapour, from 32° to 107*5°. But he 

 takes no notice whatever of similar tables that had been long before con- 

 structed by Dalton, Ure, and Southern. One would suppose that he was 

 ignorant of what had been done forty years before, were it not that in a 

 previous paper on the expansion of vapour, he quotes the very paper of 

 Dalton in which the table occurs. 



In the same volume of the Manchester Memoirs, there is inserted a 

 paper by Mr. Dalton, entitled, Experiments and Observations to deter- 

 mine whether the quantity of rain and dew is equal to the quantity of water 

 carried off by the rivers, and raised by evaporation ; with an inquiry into 

 the origin of springs. 



He gives a table of the mean quantity of rain in thirty-one different places 

 in England. The common mean of the whole is 35*2 inches. But as 

 twenty-four of the places given are situated near the sea, he thinks this 

 mean above the true average quantity for England. He reckons the true 



