826 



SCIENCE. 



[N. S. Vol. XIX. No. 491. 



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 observations were 

 made by Professor Fergola and his associates. 

 The New York and Naples work was con- 

 tinued until a similar, but a more elaborate, 

 plan was put in operation by the International 

 Geodetic Association, which includes all civil- 

 ized governments. This plan involved the es- 

 tablishment of four suitable special latitude 

 stations, and rendered further work at New 

 York and Naples unnecessary. 



Energy Liberated hy Thorium: George B. 



Pegram and Harold W. Webb. 



The method used in this investigation of the 

 energy liberated by thorium due to its radio- 

 activity was to measure the difEerence 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. Uni- 

 formity of temperature in the bath was se- 

 cured by means of a rotating stirrer and care- 

 ful heat insulation. The thorium oxide was 

 cooled, so that its initial temperature was be- 

 low that of the surrounding bath. Readings 

 were taken at frequent intervals, and after 

 several days the difference of temperature be- 

 came constant, with the oxide .04° warmer 

 than the bath. Several such series of obser- 

 vations were made. From the rate of change 

 of temperature and from an approximate cal- 

 culation of the heat capacity of bulb and 

 oxide, a tentative value of the heat liberated 

 was foimd; 8 X 10~ 5 gram-calories per gram 

 of thorium oxide per hour (.93 ergs per gram 

 per second), or 9 X 10~ 6 gram-calories per 

 gram of pure thorium, per hour. Further in- 

 vestigation is being made to determine these 

 values more accurately. 



Note on a Trihophosphoroscope, and the Du- 

 ration and Spectrum of Tribophosphores- 

 cent Light: Wallace Goold Levison. 

 Discs of thick pasteboard about 15 cm. in 

 diameter are evenly sanded on one or both 

 sides on a coating of liquid glue with the 



materials to be examined in powder, narrow 

 bands being sufficient and only small quan- 

 tities of the materials required. 



The disc selected is then rotated at a known 

 and usually moderate speed (twelve revolu- 

 tions per second, for example) by any conven- 

 ient mechanism, such as an ordinary rotator 

 used for illustrating the recomposition of 

 light. 



A point or brTosh of wire or other material, 

 or a piece of the same material with which the 

 disc is coated, being pressed against the 

 sanded surface, produces a trail of light which 

 extends from the point of contact in an arc 

 more or less around the disc; varying in color 

 with different materials and in length with 

 the speed, and is maintained for some time 

 unless the material is rubbed off by extreme 

 friction. A grindstone or corundum wheel 

 may often be used to advantage with hard sub- 

 stances as a substitute for the disc, since a 

 specimen held against it soon coats it with a 

 trace of the material which shows its luminous 

 trail beautifully. 



By means of the device described the in- 

 tensity of the light may be determined with 

 a photometer, its duration from the length of 

 the trail, and its spectrum delineated with a 

 spectroscope. 



The following approximate, tentative re- 

 sults of the examination of a few minerals are 

 given to illustrate its applicability. 



1. Sphalerite (1) from Utah. Light yellow 

 concretions in gray massive sphalerite. Vis- 

 ible trails are produced of respectively in- 

 creasing brilliancy and length with the tip of 

 the finger; a wooden match; the finger nail; 

 a brass wire brush; and a steel wire brush, or 

 point; of a yellow orange color, visible, with 

 the latter, at a distance of several yards and 

 extending about one quarter around the disc 

 at the above speed. Hence, the duration is 

 about 0.02 s. The spectrum is short, extend- 

 ing from about the line C to the line E and 

 embracing some red, orange, yellow, yellow- 

 green and green. (2) From another locality 

 very similar to the above in character, and 

 afforded like results. (3) Of several dark 

 colored sphalerites some showed a little light 



