288 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



tical with each other and equally magnetized and stick these needles 

 into corks which float on the surface of a tub of water, the}^ will 

 repel each other mutually in the same w^ay as the negative electrons 

 would do and in accordance with the same law. The force to group 

 them is derived from the pole of a large magnet placed above the tub, 

 the needles are attracted toward a point situated vertically below 

 the pole and for each one the horizontal component of the force of 

 attraction is evidently proportional to its distance from this point. 



The conditions imagined for the electrons are thus realized by the 

 needles, the only difference being that the grouping takes place not 

 in three dimensions, but in a plane. 



Let us brilliantly illuminate the tops of the corks and project 

 their images on a screen. You can see in this way the representa- 

 tion of this equilibrium. You can imagine that the brilliant spots 

 on the screen represent mobile electrons in the interior of a great 

 positive sphere. It can be seen that these electrons are regularly 

 arranged around a center forming, according to their number, one 

 or more concentric rings. 



Sir J. J. Thomson has worked out, with the aid of calculus, the 

 positions of equilibrium which the electrons may assume in greater 

 or less numbers, and has succeeded in explaining in this way the 

 periodic classification of elements discovered by Mendelejeff. It 

 should be noted, moreover, that this way of looking at the constitu-^ 

 tion of the atom takes account of the phenomena of light. It is im- 

 possible, however, to form any idea of the constitution of the sphere 

 over which the jDOsitive electricity is supposed to be distributed. 



Other conceptions can be imagined, and the field for hypothesis 

 will be unlimited as long as positive electricity remains as mys- 

 terious as it is now. It can even be said that the adoption of this 

 or that system of explanation is hardly more than a matter of pref- 

 erence. 



In any case, however, it is certain that the atom is of considerable 

 dimensions in comparison with the negative electron. The volume of 

 an atom is sufficient to contain billions on billions of electrons, but 

 as its mass indicates that it contains at most a few thousands, it is 

 certain that the electrons are at enormous distances from each other 

 in comparison with their dimensions. We might liken them to a 

 swarm of gnats gravitating about in the dome of a cathedral. 



In spite of our ignorance of the nature of positive electricity, 

 however, the facts acquired in the last 20 years render extremely 

 probable the hypothesis that the constitution of matter is purely 

 electrical. But, then, as all substances are made up of electric 

 charges, the atom of matter can no longer be considered as immu- 

 table, and one may say without being an alchemist that the trans- 

 mutation of matter is not a Utopian idea, 



