Prof. Wartmann on the Cooling of Electrified Bodies. 261 



Numbers of the order Mean time of cooling 1° C. of the 



of the Series. Electrified Surface. Non-electrified Surface. 



1 113"*43 10l"*28 



2 100 '50 97 *25 



3 95 -00 104 -25 



Mean .... 102 -97 100 -92 



o • in f electrified surf. . . 102*971 j-rc A'^h 



Series 1, 2, 3< , . •» , c -i™™ fditterence-f 2*05 



' ' 1 non-electrified surf. 100*92 J 



o • c, j « J electrified surf. . . 97*75 I !•«. 



Series 2and3«^ i-^jla±*.<* *~k±* ^difference -3*00 



non-electrified surf. 100 



in. 



<5 f 



a • i i o /electrified surf. . . 104*221 i-a> . -. . : 



Series 1 and 3| non . electrified surf< ^.^J difference +145 



Definitive difference + 0"*50. 

 I wished to control this result by another process, by sub- 

 stituting a secondary for a direct electric tension. A copper 

 vessel supported by a light tripod of wood was filled with olive 

 oil, a Leyden jar was placed in the centre of the liquid, the 

 exterior coating of which was in contact with the vessel and 

 the interior connected with the machine. A rod of brass 

 terminating on one side by a chain which descended upon the 

 ground, on the other side presented a ball a little distance 

 from the copper vessel in order to allow this complex appa- 

 ratus to become charged. The machine was put in motion 

 in such a manner that the deviation of the electroscope indi- 

 cated a constant tension. Two series of observations gave 9 

 for 27° of cooling. 



Height of barometer . . m *7218 

 Interior temperature . . +16 b 8 C 

 Exterior hygrometer . . 82° 



Numbers of the order Mean time of cooling 1° C. of the 



of the Series. Electrified Surface. Non-electrified Surface. 



1 28"*70 27"*96 



2 26 *48 26 *33 



Mean ... 27 -590 , 27 *145 



Definitive difference + 0''*445. 



Lastly, I wished to examine the case of porous bodies. The 

 method which I adopted as the most simple and the least 

 incorrect, after various trials, consists in placing some hollow 

 cylinders of wood, such as oak and poplar, in the centre of 

 a thin metallic grating, (that of a calorimeter of Lavoisier and 

 Laplace) but wider by three quarters of an inch, placed on 

 the wooden tripod near the machine. The cylinders were 

 made of a single piece without varnish and provided with a 



