438 



SCIENCE. 



[N. S. Vol. XIV. No. 351. 



moving charge of electricity. This experi- 

 ment was tried many years ago in the lab- 

 oratory of Helmholtz by Eowland, who 

 caused a charged disc to spin rapidly near 

 a magnet. The result was in accord with 

 the theory; the magnet moved as though 

 acted upon by an electric current. Of late, 

 however, M. Cr^mieu has investigated the 

 matter afresh, and has obtained results 

 which, according to his interpretation, were 

 inconsistent with that of Rowland. 



M. Cremieu's results are already the sub- 

 ject of controversy,* and are, I believe, 

 likely to be discussed in the Section of 

 Physics. This is not the occasion to enter 

 upon a critical discussion of the question at 

 issue, and I refer to it only to point out 

 that though, if M. Cremieu's result were up- 

 held, our views as to electricity would have 

 to be modified, the foundations of the 

 atomic theory would not be shaken. 



It is, however, from the theory of ions 

 that the most far-reaching speculations of 

 science have recently received unexpected 

 support. The dream that matter of all 

 kinds will some day be proved to be funda- 

 mentally the same has survived many 

 shocks. The opinion is consistent with the 

 great generalization that the properties of 

 elements are a periodic function of their 

 atomic weights. Sir IS'orman Lockyer has 

 long been a prominent exponent of the view 

 that the spectra of the stars indicate the 

 reduction of our so-called elements to sim- 

 pler forms, and now Professor J. J. Thom- 

 son believes that we can break off from an 

 atom a part, the mass of which is not more 

 than one- thousandth of the whole, and that 

 these corpuscles, as he has named them, are 

 the carriers of the negative charge in an 

 electric current. If atoms are thus com- 

 plex, not only is the a priori probability in- 

 creased that the difierenfc structures which 



*See Phil. 3Icrg., July, 1901, p. 144; and JoJms 

 Hopkins University Circulars, XX., No. 152, May- 

 June, 1901, p. 78. 



we call elements may all be built of similar 

 bricks, but the discovery by Lenard that 

 the ease with which the corpuscles pene- 

 trate different bodies depends only on the 

 density of the obstacles, and not on their 

 chemical constitution, is held by Professor 

 Thomson to be 'a strong confirmation of 

 the view that the atoms of the elementary 

 substances are made up of simpler parts, 

 all of which are alike.' * On the present 

 occasion, however, we are occupied rather 

 with the foundations than with these ulti- 

 mate ramifications of the atomic theory ; 

 and having shown how wide its range is, I 

 must, to a certain extent, retrace my steps 

 and return to the main line of my argu- 

 ment. 



THE PROPERTIES OF ATOMS AND MOLECULES. 



For if it be granted that the evidence 

 that matter is coarse-grained and is formed 

 of separate atoms and molecules is too 

 strong to be resisted, it may still be con- 

 tended that we can know little or nothing 

 of the sizes and properties of the mole- 

 cules. 



It must be admitted that though the fun- 

 damental postulates are always the same, 

 different aspects of the theory, which have 

 not in all cases been successfully combined, 

 have to be developed when it is applied to 

 different problems ; but in spite of this 

 there is little doubt that we have some 

 fairly accurate knowledge of molecular 

 motions and magnitudes. 



If a liquid is stretched into a very thin 

 film, such as a soap bubble, we should ex- 

 pect indications of a change in its properties 

 when the thickness of the film is not a 

 very large multiple of the average distance 

 between two neighboring molecules. In 

 1890 Sohncke f detected evidence of such a 



*For the most recent account of this subject see 

 an article on ' Bodies Smaller than Atoms, ' by Pro- 

 fessor J. J. Thomson in the Popular Science Ilonthly 

 (The Science Press), August, 1901. 



t Wied. Ann., 1890, XL., pp. 345-355. 



