October 10, 1903.] 



SCIENCE. 



493 



Faraday and Maxwell. Above all, it lacks 

 its Kepler. Let me make this clear. Kep- 

 ler's contribution to physical astronomy 

 was to formulate laws which no heavenly 

 body actually obeys, but which enabled 

 Newton to deduce the law of gravitation. 

 The first great step in the development of 

 any physical science is to substitute for 

 the indescribably complex reality of nature 

 an ideal system that is an effective equiva- 

 lent for the purposes of theoretical compu- 

 tation. I can not refrain from quoting 

 again from Plato's 'Republic' a passage 

 which I have quoted elsewhere. It ex- 

 presses paradoxically but still clearly the 

 relation of natural philosophy to nat- 

 ural science. In the discussion of the 

 proper means of studying sciences Socrates 

 is made to say : ' We shall pursue astronomy 

 with the help of problems just as we pur- 

 sue geometry : but we shall let the heavenly 

 bodies alone if it is our design to become 

 really acquainted with astronomy.' What 

 I take to be the same idea is expressed in 

 other words by Rayleigh in the introduc- 

 tion to his 'Sound.' He there points out 

 as an example that the natural problem of 

 a sounding tuning-fork really comprises 

 the motion of the fori, the air and the 

 vibrating parts of the ear; and the first 

 step in sound is to simplify the complex 

 system of nature by assuming that the 

 vibrations of the fork, the air and the ear 

 can be treated independently. Frequently 

 this step is a most difficult one to take. 

 What student of nature, contemplating the 

 infinity of heavenly bodies and unfamiliar 

 with this method of idealism, would imagine 

 that the most remarkable and universal 

 generalization in physical science was ar- 

 rived at by reducing the dynamics of the 

 universe to the problem of three bodies? 

 When we look round the sciences each has 

 its own peculiar ideals and its own physical 

 quantities: astronomv has its orbits and 



its momentum, .sound its longitudinal 

 vibration, light its transverse vibration,, 

 heat its energy and entropy, elec- 

 tricity its 'quantity' and its wave, but 

 meteorology has not yet found a satisfac- 

 tory ideal problem to substitute for the 

 complexity of nature. I wi.sh to consider 

 the aspect of the science from this point of 

 view and to recall some of the attempts 

 made to arrive at a satisfactory modifica- 

 tion of reality. I do not wish to refer to 

 such special applications of physical rea- 

 soning as may be involved in the formation 

 of cloud, the thermodynamics of a mixture 

 of air and water vapor, the explanation of 

 optical or electrical phenomena, nor even 

 Helmholtz's application of the theory of 

 gravitational waves to superposed layers of 

 air of different density. These require 

 only conventions which belong already to 

 physics, and though they may furnish sug- 

 gestions, they do not themselves constitute 

 a general meteorological theory. 



The most direct efforts to create a general 

 theory of atmospheric circulation are those 

 which attempt to apply Newtonian dynam- 

 ics, with its more recent developments on 

 the lines of hydrodynamics and thermo- 

 dynamics. Attempts have been made, 

 mathematical or otherwise, to determine 

 the general circulation of the atmosphere 

 by the application of some form of calcula- 

 tion, as.suming only the sun and a rotating 

 earth, with an atmosphere, as the data of 

 the problem. I confess that these attempts, 

 interesting and ingenious as they are, seem 

 to me to be somewhat premature. The 

 'problem' is not sufficiently formulated. 

 When Newton set to work to connect the 

 motions of the heavenly bodies with their 

 causes, he knew what the motions of the 

 heavenly bodies were. ^lathematies is an 

 excellent engine for explaining and con- 

 firming what you know. It is very rarely a 

 substitute for observation, and before we 



