176 Britain's Heritage of Science 



Most distinguished among the Directors of the British 

 Survey was Alexander Ross Clarke (1828-1914), who has 

 given us the most accurate determination so far obtained of 

 the size and figure of the earth. He was concerned in several 

 of the principal measurements of meridional arcs, and in 

 1860 was entrusted with the comparison of the national 

 standards of different countries, a most delicate piece of 

 work, which required the building of a separate room at the 

 Ordnance Survey Office. 



Our account of the progress of Meteorology must be short 

 and incomplete, but we may recall William Charles Wells 

 (1757-1817), the London doctor who first gave the correct 

 explanation of the formation of dew, Luke Howard (1772- 

 1864), who classified the clouds, and John Apjohn (1796 

 -1880), who showed how to calculate the humidity of the 

 air from observations with the wet and dry bulb thermo- 

 meter. We must also remember the wonderful balloon ascents 

 of James Glaisher (1809-1903), who, reaching a height of 

 over 30,000 feet, obtained the first observation of the 

 upper air. A kite was used in meteorological work as early 

 as 1749 by Alexander Wilson, of Glasgow, and its modern 

 application dates from the experiments made in England 

 in 1882 by E. D. Archibald. One of the most enthusiastic 

 workers in Meteorology, Alexander Buchan (1829-1907), 

 studied at Edinburgh and was engaged for some time as a 

 school teacher, but in 1860 he was appointed secretary of 

 the Scottish Meteorological Society, and was henceforward 

 able to devote himself entirely to his favourite study. His 

 work on atmospheric circulation possesses considerable im- 

 portance, and he was also one of the chief promoters of the 

 observatory which, during a number of years, stood on the 

 summit of Ben Nevis. 



A discovery of great value to meteorology was made by 

 John Aitken, of Falkirk, who in 1883 observed that water 

 vapour always requires some nucleus to condense upon. 

 The most common nuclei are the dust particles which are 

 always present in the atmosphere, and every drop of rain 

 or particle of fog contains some solid contamination at its 

 centre. The best protection against fog is, therefore, the 

 purification of the atmosphere. The condensation of water 



