DETERMINATION OF THE SPECIFIC HEAT OF WATER. 431 



TABLE III. 
Date. November 2. | November 6. | November 8. | November 13. Mean. 
| Temperature previous . , : : ; 
to comparison. . . 10-4 13:2 1B) > 2 10:0 114 
Temperature during | | 
comparison. . . . 21:2 21:2 21:3 21:2 | 21:2 







me |} 5 m EB m 5 m. | e m 5 
2:5 | 0:0128 | 23} 0:0108 | 2:0 | 0:0137 | 1:5 | 0-0097 | 2-1 | 0:0118 
65 | 0113 | 55 | :0118 |} 65] -0132| 70) -0116] 64] -0120 
78:0 | -0104 | 69:0 | -0092 | 89:0 | :0125 | 65:0 | -0098 | 75:2 | -0105 











It appears from the table that the thermometer suddenly plunged into water at a 
temperature of about 10° higher than that to which it was previously exposed, will, 
during the first hour show a gradual lowering of its indications, corresponding to the 
lowering of its zero point, amounting to about 0°-0012. Even after the first hour 
the change will not be complete, as is seen from Table III. ; the experiments made on 
Dec. 13 and 19 showing that after two hours and a half, the zero is still too high by 
about 00018. The first indications of the thermometer must have been too low 
therefore by about 0:004. As the total change of zero corresponding to the rise from 
11°-4 to 21°-2 is 0°009, it follows that about half the depression takes place in the 
first few minutes, 
In view of these experiments we conclude that the zero of a thermometer of 
French glass used in calorimetric determinations may after the lapse of a few minutes 
be assumed to have a position half-way between those corresponding to the lower and 
the higher temperatures. The extreme uncertainty of this range is less than one 
patt in two thousand, but it is practically certain that an error of more than one 
part in five thousand cannot be introduced by the assumption made. 
The Thermometers. 
We used as primary standard a thermometer made by Tonnexor (No. 4929). A 
complete calibration and examination of this instrument was made for us by the 
“ Bureau International des Poids et Mesures” at Paris. The thermometer is divided 
into tenths of a degree, the length of each degree being 0°58 centim. The divisions 
are beautifully sharp and can be read both in front and behind the mercury thread. 
The stem is cylindrical and has a diameter of -45 centim. The bulb has a length of 
4°8 centims. and a diameter very nearly equal to that of the stem. 
