394 ME. W. HOPKIXS OX THE COXSTEUCTIOX OF A XEM' CALOEDIETEE 
then will -KTi+Ta) be the mean temperature of the radiating suidace during the expe- 
riment, and Eg — El will = the rise in the temperature of the calorimeter during the 
observed time of the experiment, expressed in the number of beats of the watch. The 
time was usually taken longer or shorter, according as the rise of the thermometer of the 
calorimeter was slower or faster. Five hundred beats corresponded to 3-333 minutes. 
It will be observed that in each of the experiments (1), (2), &c. in each series I., II.. 
&c., the temperatures of the radiating surface are approximately equal. These experi- 
ments, (I), (2), &c., are in fact repetitions of nearly the same experiment, made with the 
view of obtaining the mean result of several experiments instead of rehing on the result 
of one. And here I may remark that this was necessary, not merely for the elimination 
of errors of observation, but also for that of the actual irregularities in the rising of the 
mercury in the thermometer of the calorimeter. Moreover no high temperatrrre can be 
maintained perfectly statiorrary, but is always in a state of oscillation about a mean valrre. 
If every experiment could be made exact, the numbers registered in the fourth column 
of the following Table ought to be the same. The irregularities which they present ar'e 
partly due to the slightly ditferent temperatures (as exhibited in the second and thud 
columns) at which the experiments were made, partly to the cairses jrrst mentioned, and 
partly to the necessary errors of observation. All these irregrrlarities may manifestly 
be more or less eliminated by taking the mearr result derived from a nrrmber of similar 
experimerrts. For this purpose I have taken the mean (T) of the tabrrlated valrres of 
Ti and Tg, arrd the mearr (E) of the values of E, and Eo, and considered (T) — (E) as 
the difference between the temperature of the radiating sruface and that of the lower 
blackerred sirrface of the calorimeter to which the heat emanating from the radiatirrg 
surface was immediately corrrmunicated ; while the rrrearr of the rrumbers in the foruth 
columrr is takeir as the corresponding rise in the temperatrrre of the calorimeter. Arr 
inspection of these columns will show how far the result of each indiridrral experirrrent 
differs from the mearr result, and will afford a rrreasrrre of the rehance which may be 
placed on this mode of experimerrtirrg. 
