334 Messrs. Wright and Kennie on the Determination of 



of the thermometers employed, and of the stirrers ; these latter 

 consisted of annular horizontal metallic plates, with stout 

 vertical wires attached, so that by moving them up and down 

 a very effective agitation could be accomplished. The ther- 

 mometers were graduated in millimetres, and were carefully 

 calibrated and checked against one another and against a 

 Kew-standardized thermometer. The one used for the inner 

 vessel was found to be sensibly uniform in calibre at the part 

 where the observations were made (chiefly that corresponding 

 to 12°-20° C); and at this part the value of 1° C. was 11*28 

 millims. Several careful determinations of the water-equiva- 

 lent of the calorimeter (including the stirrer, thermometer- 

 bulb, and voltameter, which always contained 20 grammes of 

 acidulated water containing 22 per cent, of H 2 S0 4 ,) gave 

 numbers varying from 1092 to 1097, and averaging 1094*5 

 grammes when 1000 grammes of water (weighed in a vacuum) 

 were placed therein. 



41. In order to obtain with as great a degree of accuracy 

 as possible the corrections for radiation with this instrument, 

 a large number of observations were made of the rate of al- 

 teration of the reading of the calorimeter-thermometer under 

 various conditions, viz. when the water jacket was hotter or 

 colder than the calorimeter, and when the calorimeter was 

 warmer or colder than a thermometer-bulb placed a few inches 

 above the outer lid, so as to indicate the temperature of the 

 air together with the effect produced by radiation from the 

 hand during stirring. It was found that all the observations 

 could be expressed with a fair degree of accuracy by the for- 

 mula 



x>=0'W (M-m) + 0\0225N, 



where x is the alteration of the calorimeter-temperature (loss 

 of heat) in millimetres per hour, M the difference between the 

 average readings of the calorimeter and water-jacket thermo- 

 meters during the period of observation, m a small correction 

 (derived from a specially constructed table) to reduce the scale- 

 reading of the second of these thermometers to that of the 

 first, and N the difference between the average temperature 

 of the calorimeter and that of the air, as indicated by the 

 third outer thermometer and expressed in terms of the scale 

 of the calorimeter-thermometer. Thus, for example, the fol- 

 lowing table illustrates the observed and calculated values of 

 x. It is noticeable, en passant, that whilst the heating or 

 cooling effect of the air on the calorimeter exerted through 

 the double lid is, for equal differences of temperature, much 

 less than that of the water jacket, it is still not negligible, 

 amounting to about \ of that of the jacket. 



