3^ PRESIDENTIAL ADDRESS SECTIOiN A. 



Descartes, of Brittany (1596-1650), and Huyghens, of the Ha.iiue 

 (1629-1695). Descartes considered that one of the chief ends 

 of philosophy was the complete mechanical explanation of 

 nature : and he was sanguine of being able to achieve his end. 

 He reasoned that all space must be occupied by matter imper- 

 ceptible to the senses, but a necessary vehicle for force and ligiit. 

 In the absence of experimental data, he could only reach his 

 ambition by generalizing on insufficient facts. If Newton's less 

 ambitious but more accurate work had not within 50 years cor- 

 rected Descarte's dreams, these might well have led Science 

 astray. Yet Descartes' theories on a space dominated b\- sys- 

 tems of vortices were the foundation of the cctlier on which the 

 chief modern developments have been built, and his happy intro- 

 duction into geometry of co-ordinates for expressing algebraically 

 the position of a point is essential to all accurate consideration 

 of space relations. Huyghens was the author of the wave theory 

 of light which Newton could not accept, but which is now fullv 

 established. Huygens also first perceived the principle of the 

 Conservation of Energy, which has become a most i)owerfui 

 weapon for dealing mathematically with the mysteries of physics. 

 This great principle, which has been (erroneously) c|uoted as a 

 greater triumph than the law of gravitation itself, is a striking 

 instance of the debt ofphysics to mathematics. Galileo obtained 

 the two well-known equations connecting velocity. dis])lacement 

 and time (v = ft and 5 = /4/i"). Now the elimination of t be- 

 tween these two equations is a step of the purest mathematics — 

 a step (juite independent of any physical meaning in the symbols. 

 The result i'- = 2 fs is born without a shred of physical meaning, 

 and from it follows, by adding the idea of mass, the following- 

 general result: " The increase in the value of ^ mass, (vel)- is 

 ecjual to the product of a force into the distance through which 

 it acts." Now this jumble of words has. to the non-mathematical 

 minil, or to the uninitiated, no conceivable bearing on practical 

 affairs. But we have a simple way of deceiving our non- 

 matliematical critics, and gaining their support to our conclusions. 

 We call a lump of symbols like " }/> mass, (z'el)-" and "force 

 X distance " by sweet-smelling words. Some genius i:)ro]xised 

 to call ^ mass. (z'el)~ "energy," and force X distance "work 

 done." Our equation then reads, " The ^'ain of (kinetic) energy 

 is equal to the work done (in any mechanical system)." Every- 

 one now agrees that this is intelligible, especially if he realizes 

 that " energy " means " the power of doing work." If words 

 less fascinating than " energy " and " work," such as " logar- 

 ithm," " momentum." " ergal," " entropy." had been coined, the 

 plain man would have kept aloof : and his mildest criticism 

 would have been, " You are talking in technical language : I can- 

 not follow vou." Now " energy " and " work " are as arbitrary 

 translations of the symbols, and as technical, as any of those I 

 have instanced. The " talking philosopher " has no more right 

 to appropriate this " equation of energy " as a " world law " 

 than the Binomial Theorem or other purely technical mathe- 



