48 



SCIENCE. 



[N. S. Vol. XII. No. 289. 



phenomena of the Lenard rays, is the one 

 usually accepted. 



The value of ejm was determined by two 

 entirely different methods by J. J. Thom- 

 son, the results being published at practi- 

 cally the same time as those of Wiechert. 

 In the first method used by Thomson, the 

 kinetic energy of the particles was deter- 

 mined by measuring the heat developed 

 when the rays fell upon the face of a ther- 

 mopile, and the charge carried by them was 

 measured by an electrometer. These two 

 measurements, together with the magnetic 

 deflection in a known field, make possible 

 the computation of both elm and v. The 

 values of e/m obtained in the most reliable 

 experiments by this method ranged from 

 14 X 10" to 10 X 10". The corresponding 

 values of the velocity were about one-tenth 

 the velocity of light. The second method, 

 which is regarded by Thomson as more reli- 

 able, involved the determination of the 

 electrostatic deflection in a known electric 

 field, and the magnetic deflection of the 

 same rays in a known magnetic field. This 

 method gave values of e/m ranging from 

 9 X 10" to 6.7 X 10", the velocity being about 

 one-tenth that of light, as before. Thomson 

 found that the ration e/m was independent 

 of the nature of the gas in the tube. This 

 result has been confirmed by Kaufmann,* 

 who found that the ration was also inde- 

 pendent of the material of the kathode. 



The conclusions naturally drawn from 

 these results may be put into the following 

 crude and provisional form : The kathode 

 rays coQsist of negatively charged particles, 

 or corpuscles, which are much smaller than 

 the atom of hydrogen. These corpuscles 

 are present as a constituent part of the 

 molecule in all substances: whether only 

 one such corpuscle is present for each mole- 

 cule, possibly revolving about it like a satel- 

 lite, or whether each molecule consists of 

 an aggregation of corpuscles, it is not yet 



* Wied. Ann., 61, p. 545, 1897. 



possible to say. Under the influence of the 

 intense electrical field at the negative ter- 

 minal of a vacuum tube, the corpuscles are 

 in some cases freed from the forces that 

 hold them to the remainder of the mole- 

 cule, and shoot off at enormous speed to 

 form the kathode rays. 



Ernest Mereitt. 

 CoENELL University. 



( To he concluded. ) 



S03IE TWENTIETH CENTURY PB0BLE3IS.* 

 It is never a bad plan to improve an an- 

 niversary occasion by comparative observa- 

 tions. In commercial and manufacturing 

 lines, short intervals of time are marked by 

 balancing books and checking off accounts, 

 and an inventory is taken at the end of the 

 year without exception. And so it happens 

 that I am going to recognize to-day the 

 fact that we stand at the end of a century, 

 and what I have to say will be influenced 

 to no small extent by the recognition of 

 that fact. 



Under ordinary circumstances, with this 

 in mind, I could hardly avoid following the 

 commercial example at the end of the year, 

 and taking an account of stock, balancing 

 accounts, and ascertaining the advance or 

 retrogression in our branch of the scientific 

 world during the period of time that repre- 

 sents three generations of human beings. 

 I do not intend, however, to do this, partly 

 because I do not wish to weary an audience 

 with all that ought to be passed in review 

 in such an important anniversary summa- 

 tion, and partly because, a few years since. 

 Professor H. Marshall Ward, in resuming 

 the botanical progress of the Victorian Era, 

 gave the more important facts, while the 

 vice- presidential addresses of several recent 

 years before this Section have dealt with 

 important advances in botanical thought in 

 *Address of tbe Vice-President, Chairman of Sec- 

 tion G (Botany) of the American Association for the 

 Advancement of Science, given at the New York 

 meeting. 



