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Mr. E. J. Stone on the Heating -Powers of [Jan. 13, 



1st. I have placed two very delicate thermometers, one in contact with 

 each face a and (3 of the pile, along the lines of junction of the plates. 

 The thermometers were separated from each other, and the direct radiation 

 of one on the other prevented by the interposition of a piece of blackened 

 card. The two thermometers, with faces of pile in contact, were then ex- 

 posed to the radiation of the halves of the face of the cube containing the 

 boiling water. A third delicate thermometer was read for registration of 

 any change in the temperature of the surrounding air. This thermometer 

 was protected from the direct radiation from the cube. The pile, with 

 thermometers in contact, was then placed at different distances from the 

 cube and the thermometer-readings taken. I have usually taken readings 

 at three distances, one at about 23*5 inches, another at 11*9 inches, 

 another at 2 5 inches. From a comparison of these readings with those 

 taken before the heat from the cube fell upon the thermometers, I infer 

 the heating-power of each half of the cube upon the thermometers, with 

 faces of pile in contact. Calling this quantity for one inch of distance 

 H', I find for my cube in its present state, with slightly laquered face, 

 H' = 130° F. 



2nd. If H denote the corresponding heating-power of each half of the 

 cube upon the faces of the pile a and /3, I have found the ratio H : H' as 

 follows : — 



The thermometers being placed in contact with the faces of the pile, and 

 the galvanic connexions made, we may be certain that the temperature of 

 the thermometers has been imparted to the faces of the pile when the 

 needle is steady, provided that the current be carried from the thermo- 

 meters without loss in the nature of increased resistance. I have there- 

 fore compared the deviations produced by glass G before the faces /3 and a 

 with the thermometers in contact and without thermometers in contact 

 with two different amounts of resistance in circuit. Such observations 

 have been considered satisfactory only when the two resistances for ther- 

 mometers in contact and without thermometers are sensibly equal. This 

 condition can be obtained by making the thermometers touch along the 

 lines of junction of the antimony and bismuth ; but the connexion being 

 one of mere contact, there is always danger of failure. 



The following observations were made on 1869, Aug. 19 : — 



1. Without thermometers : 



Resistance = R + 0*003 B.A. units. 



Mean difference, G before /3 — G before a =735 div. 



2. With thermometers in contact : 



Resistance = R : + 0*003 B.A. units. 

 Mean difference =698 div. 



3. With thermometers in contact : 



Resistance =R X + 1*437 B.A. units. 

 Mean differences = 324 div. 



