70 



SCIENCE 



[N. S. Vol. L. No. 1281 



of lead toward the force of gravitation. 

 Whether or not this is so may easily he ascer- 

 tained through physical tests which might pre- 

 ferably be in the nature of comparative 

 pendulum measurements, lead derived from 

 uranium ore being obtainable in sufficient 

 quantities for the purpose. 



The generally accepted law according to 

 which the ratio of weight to mass has a fixed 

 value in the same locality, irrespective of the 

 nature of the substance, is largely empirical, 

 as there are a number of elements for which 

 the law has never been proved. Considering 

 the very irregular distribution of other prop- 

 erties, like magnetism and radioactivity, among 

 the elements it would not be surprising if devi- 

 ations were found to exist in their gravita- 

 tional properties as well. 



From this point of view, i. e., if deviations 

 actually exist in the value of gravitational 

 acceleration for the various forms of lead, the 

 chances are that the value in any case will 

 be proportional to the atomic weight, as in this 

 instance the atomic mass, being the ratio of 

 either, would come out the same for all forms 

 of lead. Such a result would go far toward 

 reconciling the discrepancies in atomic weight 

 with already established theories, because 

 what is really of interest, both from a physical 

 and chemical standpoint, is not so much the 

 weight of the atom as its mass. Weight is only 

 an attribute of mass, the latter having long 

 been recognized as the more basic entity. 



The theories on gravitation are still in a 

 crude shape, but if the attraction is assiuned 

 to be due to the movements of the electrons 

 constituting the atoms a possible deviation in 

 the gravitational attraction of uranium lead 

 might perhaps be ascribed to a gradually sub- 

 siding state of tension or agitation among the 

 electrons, caused by the splitting up of the 

 atoms during the radioactive processes, condi- 

 tions being thus comparable to those supposed 

 to obtain in a permanently magnetized piece 

 of steel. On this assumption uranium lead 

 would, in course of time, increase in atomic 

 weight, changing slowly into ordinary lead, 

 while the lead derived from various uranium 

 minerals might properly be considered as rep- 



resenting intermediate stages in this process 

 of relaxation. 



Anders Bull 

 Brooklyn, N. T. 



WORKING UP IN A SWING 



To THE Editor of Science : Mr. A. T. Jones 

 has an article on this subject in the current 

 volume of Science, p. 20, July 4, 1919. In 

 the beginning he makes a statement as fol- 

 lows: 



As I do not recall ever seeing any discussion of 

 this matter, the following note may not be out of 

 place. 



I wish to call Mr. Jones's attention to E. J. 

 Routh's "Dynamics of a System of Eigid 

 Bodies" (Macmillan), Yol. I., Art. 287, en- 

 titled " Examples of Living Beings." In ex- 

 ample 6 he will find a complete solution of 

 his problem, with the necessary mathematical 

 equations. 



V. Karapetoff 



Cornell TjNnrEEsnrr, 

 July 8, 1919 



To the Editor of Science: The letter in 

 Science of July 4, by Professor Arthur Taber 

 Jones, on " working up " in a swing, recalls to 

 the writer that while studying the problem 

 several years ago he found several references 

 to the subject. 



In the Zeitschrift fur physihalischen und 

 chemischen Unterricht, 16, 230 1913, H. 

 Lohmann describes an apparatus by means of 

 which the process of " working up " may be 

 demonstrated. This consists of a plunger 

 electromagnet, suspended as a pendulum, with 

 its axis vertical. liaising and lowering the 

 center of gravity of the suspended mass is ac- 

 complished by means of a key which controls 

 the position of the plunger within the sole- 

 noid. The circuit is closed, and the plunger 

 (and therefore the center of gravity) is raised 

 when the key is in the "up" position; the 

 plunger drops a short distance when the key 

 is depressed. By imagining himself in a 

 swing, the operator has no difficulty in so 

 manipulating the key that the raising and 

 lowering of the center of gravity of the swing- 



