THE DEVELOPMENT OF METEOROLOGY. 43 
exists and when it does not exist. In 1851-55 appeared the 
memoir of Stokes on viscosity, and in 1857 the famous 
memoir of Helmholtz on vortex motions, each of which re- 
moved difficulties that had hitherto obstructed our progress. 
The works of Sir William Thomson, now Lord Kelvin, on 
thermodynamics and on circulatory motion, and the persist- 
ent researches of BjerknevS, father and son, in the application 
of vector analysis, have clarified our ideas and represent our 
present highest attainments in this branch of mechanics. 
Just as meteorologists have hitherto been dependent upon 
physicists for the apparatus with which to observe, and upon 
the mathematical physicists for the explanation of the opti- 
cal and thermal, the acoustic and the electric phenomena of 
the atmosphere, so now they are coming to be more and more 
dependent upon the higher mathematics to resolve the an- 
alytical difficulties inherent in the complex problems of fluid 
motion. 
It is very rarely that the meteorologist arrives at a phe- 
nomenon deductively and then examines the records of ob- 
servation to see if it actually exists. Ferrel did this in a few 
cases; but usually we have proceeded by slow inductive 
methods. For instance, the Phoenician voyagers and the 
Greeks who penetrated into India knew of the existence of 
the southwest monsoon, but a complete knowledge of its 
origin and nature has required centuries of observation and 
the labors of men of great talent in mechanics. Fifty years 
ago it was assumed in a general way that the heated air over 
the interior of Asia, by expanding and overflowing, gave 
rise to an indraft corresponding to the southwest monsoon; 
but it remained for Ferrel, about 1880, to show that it was 
not merely a heated interior, but a heated high plateau that 
was necessary to produce this great current; and it was not 
until 1890 that Sir John Eliot showed that this monsoon 
current is by no means a simple disturbance of the northeast 
trade winds that are appropriate to the latitudes of India, 
but that we have to go much farther south, far across the 
equator, and see that the whole southeast trade-wind system 
of the southern Indian Ocean is perverted from its course. 
7— Bull. Phil. Soc., Waeh., Vol. 16. 
