1 82 GREAT MEN OF SCIENCE 



Dalton was born in a village in the north-west of England, 

 where his father was a weaver and also leased a small 

 estate. He was taught in a neighbouring school, but already 

 became at the age of thirteen a teacher in his birthplace, 

 where he also helped his father on the farm. From then on 

 he earned his living all his life as teacher in various schools, at 

 the same time always working further on his own education 

 by means of the help of friends. He soon published 

 some original work on mathematical questions. At the age 

 of twenty-seven he went to Manchester, which remained 

 his permanent home. His activity as a teacher provided him 

 with sufficient for his modest needs; he did not found a family. 



His experimental investigations were carried out with 

 simple means; they related mostly to gases and vapours. It 

 was natural, since temperature measurement by means of 

 mercury thermometers had been developed, that the investi- 

 gation of the behaviour of the air and also of that of water 

 vapour at various temperatures began. In particular, the re- 

 lationship between volume and pressure, and the tempera- 

 ture, was examined; but many contradictory statements were 

 in circulation. Dalton was the first to produce thorough 

 results. Vapours were investigated in barometer tubes, in 

 which he allowed the liquid which was to form the vapour to 

 rise to the surface of the mercury; the tubes were then ex- 

 posed to various temperatures. He found that for every 

 temperature a corresponding definite pressure of the vapour 

 exists, which is quite independent of the quantity of excess 

 liquid, and of the volume of the vapour. This is the funda- 

 mental fact concerning vapours, which determines all matter 

 of evaporation, condensation, and boiling; it was Dalton's 

 original discovery, and he already produced tables of vapour 

 pressure. He also found that the vapour pressure corres- 

 ponding to the temperature is also present unchanged, even 

 when at the same time a gas is present in the space. The 

 pressure of the gas, which is determined by the law of Boyle 



