[Footnote 1: In our case the heat-capacity, thermometer included, was 0.0757; total, 0.1053; radiation, etc., 0.0296. Respectively, 71.9 per cent, and 28.1 per cent. of the total.]
Four experiments, carefully conducted, gave the following results:
Loss of temperature by pouring at 170° F., 0.81°, 0.86°, 1.00°, and 1.07° F.; mean, 0.935° F.
The following are values of the calorific capacity of my pyrometers, that is, of those parts of each which share directly the temperature of the inclosed water, including the thermometer to be used with the instrument, and the heat communicated to the eider-down and otherwise lost during an observation, expressed in decimals of a British thermal unit, or in decimals of a pound of cold water:
0.1048, 0.1052, 0.1077, 0.1008, 0.1028, and 0.1104.
Mean 0.1053 = 0 lb. 1 oz. 11 drms.
Add water 1.8947 = 1 " 14 " 4 "
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2.0000 = 2 " 0 " 0 "
This was the value used. The instrument, being put on delicate coin scales and counterbalanced, weights equal to 1.8947 lb. avoirdupois = 1 lb. 14 oz. 5 drms., were added to the counterbalancing weights, and cold water was poured in until the scales again balanced.
The pyrometer with its contained water was then just equal in heating capacity, while the temperature was not above 38° F. to two pounds of cold water. The two instruments were sensibly alike, but were numbered No. 1 and No. 2, and at each observation the one used was noted.
The process of preparation and testing appears long and tedious, and is indeed somewhat so; but the instruments once well made are durable, convenient in use, and with care reasonably accurate.
Compared with mercurial thermometers between 212° and 600° F., I believe them to be much more accurate, although less convenient.