September 11, 1903.] 



SCIENCE. 



347 



RADIVM. 

 The London Times publishes a report of a 

 paper which M. Curie has comnuinicated to 

 the French Physical Society. It appears that 

 at the time of his lecture at the Royal Institu- 

 tion in June, the resources of that laboratory 

 in producing and manipulating liquid gases 

 were utilized in a new series of experiments. 

 Professor Dewar had already in 1893 improved 

 the calorimetric use of liquid gases by means 

 of a combination of vacuum, vessels so that 

 . heat-evolution at the temperature of boiling 

 liquid air or hydrogen could be determined 

 with accuracy. When a sample of radium 

 bromide weighing 0.7 gramme was tested in 

 this way it was found to be capable of volatiliz- 

 ing an amount of liquid oxygen and hydrogen 

 equivalent respectively to 6 c.c. and 7-3 c.e. of 

 the gases measured at the ordinary tempera- 

 ture. It seems that through a very wide range 

 of temperature the thermal emission remains 

 unchanged. Wliether at the temperature of 

 a summer day or at that of liquid air, the 

 emission of heat goes on without perceptible 

 variation. 



When, however, we make a long downward 

 stride from liquid air to liquid hydrogen, 

 radium shows that it is not always unafiFected 

 by external temperature. Within a compara- 

 tively short distance of the absolute zero a 

 change occurs in the rate of heat-emission, 

 but not in the direction that might be antici- 

 pated in view of the effect of low temperatures 

 on ordinary chemical action. Instead of be- 

 ing reduced, the emission of heat, so far as 

 present data can be relied on, is augmented 

 at the temperature of liquid hydrogen. What- 

 ever be the nature of this extraordinary phe- 

 nomenon, it only increases in intensity at a 

 point where all but the most powerful chemical 

 affinities are in abeyance. The evaporation of 

 a liquid gas gives an absolute measurement of 

 the amount of heat given off by radium. 

 Changes in the degree of radio-activity may 

 escape the most careful observer, or may be 

 imagined where they do not exist, but the 

 quantity of liquid hydrogen which a given 

 mass of radium converts into gas in a given 

 time can be easily measured with an accuracy 



which is beyond cavil, and the amount of heat 

 required for the conversion can be ascertained 

 with great precision. Hence there is no 

 longer any doubt either of the quantity of heat 

 evolved by radium or of the fact that the rate 

 of emission is apparently greater in liquid 

 hydrogen than at any temperature from that 

 of liquid air up to that of an ordinary room. 

 At the beginning of these experiments in 

 liquid hydrogen a contrary result appeared to 

 emerge when the low-temperature thermal 

 measurements were compared with the early 

 Curie values observed at the temperature of 

 melting ice, as formerly given in The Times. 

 This led to the curious discovery that a 

 freshly prepared salt of radium has a com- 

 paratively feeble power of giving off heat at all 

 temperatures, but that its power steadily in- 

 creases with age imtil about a month from its 

 preparation, when it reaches the maximum 

 activity, which it afterwards maintains ap- 

 parently indefinitely. A solution of a radium 

 salt behaves in exactly the same way. Its 

 power of heat-emission is at first relatively 

 low, but goes on increasing for about a month, 

 when it becomes equal to that of the solid 

 salt, and so remains. 



MAGXETIC WORK EXECUTED BY THE V. 8. 



COAHT Ayo GEODETIC SURVEY BE- 



TWEES JULY 1, 1902, AXD JUNE 



;w, 190,1. 



The work accomplished during the fiscal 

 year, July 1, 1902, and June 30, 1903, may 

 be summarized as follows : 



A. Magnetic Survey WorJc. — The magnetic 

 elements were determined at 461 stations dis- 

 tributed over thirty-one states and territories, 

 three foreign countries and adjacent seas. 

 The principal work was done in Arizona (54 

 stations), Florida (26), Kansas (49), Louisi- 

 ana (15), Maryland (8), Michigan (14), 

 Nebraska (19), Ohio (19), Pennsylvania (52) 

 and Texas (72). 



By December of this year, owing to the prog- 

 ress already made, the magnetic survey of the 

 area bounded by latitudes 35° and 41°, and 

 longitudes 75° and 85°, embracing the states 

 of Pennsylvania, Xew Jersey, Delaware, Mary- 

 land, Virginia, West Virginia, Ohio, North 



