492 



Mr. H. Tomlinson. The Influence of 



placed close to the end F of the air-chamber, and the double screen 

 MM having been first removed the cork F was pulled out, and after 

 it, through the intervention of the thread, the brass envelope with 

 the contained wire, which were speedily dropped into the calorimeter. 

 After the water in the calorimeter and its contents had been stirred 

 for three minutes, the temperature of the mixture was determined to 

 within y-jy-Q- C. by means of the first of the previously-mentioned 

 thermometers, care having been taken by means of the erection of 

 certain marks to avoid parallax in the reading. After the first reading 

 had been taken two others ensued after successive intervals of three 

 minutes each, so that correction might be made for loss of heat 

 resulting from radiation ; this loss, however, being almost compensated 

 by placing in the calorimeter water at a temperature which previous 

 rough calculation had shown would be as much below the temperature 

 of the room as the temperature of the mixture would be above it. 



Preliminary observations were made for the purpose of ascertaining 

 the rise of temperature which would be caused by immersing the 

 heated envelope only in the 450 grams of distilled water used in the 

 calorimeter, and the mean of eighteen observations in which the 

 envelope alone was raised to 60° C. and then plunged into water at 

 about 20° C, showed that the average rise of temperature per degree 

 of fall of temperature of the brass envelope between 60° C. and 20° C. 

 was OOHSO C. Similarly eighteen observations between 100° C. and 

 20° 0. showed a rise of 0'01114°C. to be produced per degree of fall 

 of temperature of the envelope. If the thermal capacity of the brass 

 of which the envelope was formed be assumed to be O0924 between 

 20° O. and 60° C.,* the calculated rise of temperature, supposing that 

 no heat is lost in the transference of the envelope from the air-chamber 

 to the calorimeter, would be 0'0137 ; so that, as might be expected 

 from the large surface of the envelope as compared with its mass, the 

 loss of heat during the transference is very appreciable, and, as also 

 might be expected, the loss between 100° C. and 20° C. is greater than 

 that between 60° C. and 20° C. It will be sufficient, perhaps, to 

 record the eighteen observations between 20° C. and 100° C. 



* My subsequent experiments would prove that this would be very nearly the 

 case. 



