398 Intelligence and Miscellaneous Articles. 



temperature o£ 1500°, from the Martin- Siemens furnace. If we 

 assume that the mean emissive power of the sun is sensibly equal 

 to that of steel in fusion, determined (as I hare just said) in the 

 identical conditions of my experiments on the sun*, we arrive at 

 the value of 2000° for the true mean temperature of the solar sur- 

 face. — Comptes Rendus de V Academic des Sciences, vol. lxxix. pp. 

 746-749. 



PRELIMINARY NOTICE ON A NEW METHOD FOR MEASURING THE 

 SPECIFIC HEAT OF GASES. BY EILHARD WIEDEMANN. 



Since the researches made by M. Eegnault, no physicist has re- 

 sumed in a thorough manner the study of this important question 

 — perhaps on account of the complication and large dimensions of 

 the apparatus to be employed. Kow I have succeeded in discover- 

 ing a method which realizes, with means much more simple, an 

 accuracy as great as that arrived at by M. Eegnault with his. 



The gas to be studied is enclosed in a balloon of caoutchouc con- 

 taining about 25 litres kept in an empty balloon of glass by means 

 of a glass tube fixed in a caoutchouc stopper. Another tube serves 

 to put the glass balloon in communication with a second balloon, 

 which communicates with a reservoir full of water placed 10 feet 

 above. A manometer gives the pressure in the interior of the 

 second balloon. "When water is brought from the reservoir into 

 this balloon, the air found there is compressed, and the pressure is 

 transmitted to the caoutchouc balloon. A certain quantity of the 

 gas is thus expelled from the caoutchouc balloon into the heating- 

 apparatus and the calorimeter. This quantity can be measured ex- 

 actly by the weight of the water introduced, account being taken 

 of the temperature and the pressure. 



The heating-apparatus consists of a tube 3 metres long and 9 cen- 

 tims. in diameter, completely filled with copper turnings, and placed 

 in a leaden tank full of boiling water. The heating of the gas is 

 complete when 10 litres of it traverse the apparatus per minute. 



The calorimeter is composed of a series of tubes of silver 43 mil- 

 lims. in height and 9 millims. wide, filled with silver turnings, and 

 successively traversed by the gas. These silver tubes, three in 

 number, dip into a cylindrical vessel of silvered copper 54 millims. 

 in height and 44 millims. in width, full of water. Prom the rise 

 of temperature undergone by this water, the equivalent in water of 

 the vessel and the tubes being known, the quantity of heat given 

 up by the gas, and its specific heat, can be deduced. 



To avoid radiation, arrangements are made so that the tempera- 

 ture of the surrounding space shall be constant and exactly equal 

 to the mean between the initial and final temperatures of the water 



* I have, in fact, verified that, with my actinometer, the dynamic method 

 conducts to exactly the same number for the effective temperature of the 

 sun as the static method. 



