RECORDS. 329 



Series of Memoirs. To that publication the reader is referred 

 for complete details and results ; it is not possible here to do 

 more than mention very briefly the plan of the work and to 

 state the fact of its completion. 



The simultaneous and continuous observation of the same 

 stars at stations situated on a single parallel of latitude, but 

 separated widely in longitude, has long been recognized as the 

 best method of attacking the problem under consideration. The 

 first actual practical application of the method is the one treated 

 in the present paper. The other participating observatory is 

 the one at Capodimonte, near Naples, where simultaneous ob- 

 servations were made by Professor Fergola and his associates. 



The New York and Naples work was continued until a simi- 

 lar, but a more elaborate, plan was put in operation by the 

 International Geodetic Association, which includes all civilized 

 governments. This plan involved the establishment of four 

 suitable special latitude stations, and rendered further work at 

 New York and Naples unnecessary. 



The method used by Messrs. Pegram and Webb, in this in- 

 vestigation of the energy liberated by thorium due to its radio- 

 activity, was to measure the difference between the temperature 

 of three kilograms of thorium oxide, enclosed in a Dewar bulb, 

 and that of a surrounding ice-bath, by means of a set of iron- 

 constantin thermo-electric couples. Uniformity of temperature 

 in the bath was secured by means of a rotating stirrer and careful 

 heat insulation. The thorium oxide was cooled, so that its initial 

 temperature was below that of the surrounding bath. Readings 

 were taken at frequent intervals, and after several days the differ- 

 ence of temperature became constant, with the oxide .04° warmer 

 than the bath. Several such series of observations were made. 

 From the rate of change of temperature and from an approximate 

 calculation of the heat capacity of bulb and oxide, a tentative 

 value of the heat liberated was found ; 8 x io~' gram-calories per 

 gram of thorium oxide per hour (.93 ergs per gram per second), 

 or 9 X io~'^ gram-calories per gram of pure thorium per hour. 

 Further investigation is being made to determine these \'alues 

 more accuratelv. 



