300 Mr. Carl Barus on the Fusion 



reached after 5 minutes. Hence the time from 10 to 15 

 minutes was available for making the final measurements for 

 cooling ; knowing the extremes, I found the intermediate 

 rates in accordance with the law of cooling. Thus, while the 

 calorimeter was being constantly stirred, its temperature was 

 measured at the end of each minute. Hence I knew the mean 

 excess of its temperature above its environment during the 

 course of every minute, and was able to add the corresponding 

 allowance for radiation and evaporation at once. How im- 

 portant this correction is the Tables (§ 10) fully show. The 

 only drawback against sharp values is the lag error of the 

 thermometer ; but this is eliminated in a long series. 



I have stated that both the calorimeter and the crucible 

 were weighed before and after each measurement. The latter 

 data were taken. 



9. Arrangement of the Tables. — The two crucibles (§3) 

 and tubes (fig. 3) are designated I. and II. In all cases m 

 is the mass of the charge, M the calorimetric value of the 

 calorimeter (corrected for temperature), t the temperature of 

 the environment. ® is the temperature at the top, the 

 middle, and the bottom of the charge at the time of submer- 

 gence. The mean value is also given. The temperature of 

 the calorimeter at the time specified is given under 6, and a 

 parallel column shows the correction of 6 for radiation. 

 Finally, the computed thermal capacity of the platinum cru- 

 cible and appurtenances (correction 7i), and the thermal 

 capacity* h of the charge computed up to each of the con- 

 secutive times, are found in the last columns. A few obvious 

 remarks follow. Note that h reaches its true (constant) value 

 in proportion as the body is cold. 



To avoid prolixity I have only given full examples of the 

 data here defined at the head of each table. The remainder 

 is abbreviated. 



10. Tables. — In the data of the first series (Table I.) only 

 one value of © is in hand for the liquid state. Moreover the 

 construction of the furnace was somewhat faulty, not being 

 flat-bottomed. Hence these results are of inferior accuracy 

 as compared with Series II. (Table II.), which are the best 

 obtained. 



* The constant h is really the increase of thermal capacity above zero 

 degrees Centigrade. 



