66 BULLETIN OF THE 



Mr. W. B. Taylor read a paper 



ON WAVES, MOLECULES, AND ATOMS. 

 (abstract.) 



Of the five elements necessary to complete the physical theory 

 of light and heut undulations, three are known with a tolerable 

 degree of certainty and accuracy ; to wit, the velocity of propa- 

 gation, the length of the wave, and the varying rapidity corre- 

 sponding thereto. The two remaining elements — the average 

 amplitude of the wave, and the fomn, or character of excursion 

 of a wave particle — are undetermined. 



Mr. M. Ponton has recently* attempted to estimate the ampli- 

 tude of the ethereal wave by a comparison of the velocities of 

 light and sound, and the relative energies of elasticity involved, 

 making it of the order of 500 thousand millions to the wave- 

 length, or 2000 billion to the inch ; and making the amplitude 

 proportional to the wave length. Unfortunately, this estimate 

 takes no account of the momentum or mass of the vibrator}'' me- 

 dium, an element which we have no means of determining. 



The dynamical theory of heat as applied to gases, teaches us 

 that their isolated constituent molecules, separated from their 

 mutual cohesive attractions, are at all temperatures, in a state of 

 motion and collision, not indeed of actual contact, but of impinge- 

 ment upon each other's dynasphere of repulsion ; the energy of 

 which repulsion is estimated by Maxwell as being inversely as the 

 fifth power of the distance. 



From computations made by Mr. Waterston in 185Y, by Mr. 

 Stoney in 1868, and by Sir William Thomson in 18*70, all tole- 

 rably concordant, we may accept the order of magnitude of the 

 molecules as being in the neighborhood of the 200 millionth of 

 an inch. The conjoined calculations of Clausius and Maxwell 

 have rendered it probable that at ordinary temperature and pres- 

 sure the average length of free excursion of the molecules of a 

 gas between collisions, is about 300 thousand to the inch, the 

 mean velocity at the rate of 1640 feet per second, and the fre- 

 quency of collisions, consequently, about 6000 million per second. 

 These motions are, however, exceedingly variable and irregular, 

 both in the lengths and in the velocities of the excursions ; and 

 therefore take no part in impressing the ethereal medium, or in 

 the production of light. 



Each molecule is a remarkably constant and complex structure, 

 consisting of an aggregation of parts which may be provisionally 

 called "atoms," and which are in regular or rhythmical move- 

 ment among themselves ; and it is in this motion of the material 

 atoms that the luminiferous waves have ever their origin. We 



* Quarterly Journal of Science, July, ]871, i. 349. 



