THE KINETIC THEORY OF MATTER 439 



age displacement was far 'greater than the uncertainty in any of the 

 factors in terms of which this displacement was computed. Neverthe- 

 less, the final result obtained from the average of 1,735 displacement 

 observations on nine different drops was within less than one fourth of 

 one per cent, of the computed value, and the probable error in this re- 

 sult was but six tenths of one per cent. 



All of these computations relating to the Brownian movements 

 were carried out most skilfully bv Dr. Harvev Fletcher. It should be 

 added, too, that in only a portion of the experiments was the observed 

 value of the displacement obtained in precisely the manner indicated 

 above, for it was found that greater accuracy could be obtained in the 

 measurement of this displacement by a slight modification of the 

 method. To make this modification applicable, however, a consider- 

 able amount of new and important theoretical work had to be done. 

 This work was most ably and successfully carried out Ijy Dr. Fletcher, 

 and can be found in the August number of the Physical Review. 



It would seem as though the evidence for the kinetic theory were 

 so overwhelming as to convince every ty]3e of skeptic except the one 

 whose mental attitude is that of the farmer who had never seen any 

 save farm-yard animals until he went one day to the circus and stood 

 for some moments looking in amazement at the dromedary; then turn- 

 ing away, he exclaimed, " By gosh, there ain't no such animal." That 

 type of disbeliever I am at a loss to know how to convert. 



In conclusion it may be pointed out that not only has it now be- 

 come possible to prove the correctness of the kinetic theory of matter 

 and the granular theory of electricity, but that, through the results of 

 experiments like the aliove on the elementary electrical charge, we are 

 now able to determine the exact weight of every atom and every mole- 

 cule of every known kind of matter, the exact number of molecules in 

 any weight of any substance, the exact value of the kinetic energy of 

 agitation of a molecule, the mean diameter of any kind of molecule, 

 and quite a series of other important physical magnitudes. The first 

 three of these quantities can be found with precisely the degree of ac- 

 curacy attained in the measurement of the elementary electrical cliarge, 

 and this is an accuracy of about one part in a thousand. Not that I 

 am ready to assert that the value which has lieen given above possesses 

 that degree of certainty; but rather that we now have a method which 

 is capable of yielding such precision, and the rest is merely a matter of 



from this equation and these experiments and the value of Ne obtained from 

 experiments on electrolysis ; for Ne is merely the amount of electricity required 

 to separate by electrolysis one gram-equivalent of any substance from a solution. 

 The value of \/Ne obtained from the most accurate experiments on the elec- 

 trolysis of silver is 1.702 X 10' electrostatic units. The mean value of VNe 

 obtained from 1,735 displacement measurements upon nine different drops was 

 1,698 X 10' electrostatic units. 



