Page:Popular Science Monthly Volume 80.djvu/443

Rh displacement was far 'greater than the uncertainty in any of the factors in terms of which this displacement was computed. Nevertheless, 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 result was but six tenths of one per cent.

All of these computations relating to the Brownian movements were carried out most skilfully by Dr. Harvey 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 considerable amount of new and important theoretical work had to be done. This work was most ably and successfully carried out by 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 type 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 turning 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 become 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 above on the elementary electrical charge, we are now able to determine the exact weight of every atom and every molecule 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 accuracy attained in the measurement of the elementary electrical charge, and this is an accuracy of about one part in a thousand. Not that I am ready to assert that the value which has been 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