32 Captain Kater's account of the 



pounds of distilled water, at the temperature of 62° of Fa- 

 renheit's thermometer, the barometer being at 30 inches ; 

 consequently, for any difference from this state of the baro- 

 meter, as well as of the thermometer, a correction must be 

 applied. Water is 831 times heavier than air when the 

 barometer is at 30 inches, and the thermometer at 62°, and this 

 varies directly as the height of the barometer, consequently 

 the correction due to a difference of one inch of the barometer 

 will be -5 — X — = -^— part of the weight of water. 



831 30 24930 r & 



The gallon weight being counterpoised with brass, and 

 brass being about 8 times heavier than water, the effect of 

 the buoyancy of the atmosphere upon brass will be only ^ 

 of that upon water, and this will tend to lessen the effect 

 upon the water by one eighth part of the whole quantity. 

 Therefore — -— ^ I x 70000 grains = 2,46 grains, is the 

 number of grains by which the weight of the gallon of water 

 will be increased by a depression of one inch of the barometer. 

 Though the variation of the temperature of the air during 

 the experiments was several degrees, the effect upon the 

 correction for the buoyancy of the atmosphere would have 

 been so inconsiderable as to be unworthy of notice upon the 

 present occasion. 



As an error of one degree in the determination of the 

 temperature of the water contained by the gallon would 

 occasion an error ranging from four to six grains, it must 

 be evident that a knowledge of the precise temperature of the 

 Wjater was of primary importance. For this purpose a thermo- 

 meter was used which had been prepared with extraordinary 

 care by Mr. Bate, and the scale was such that its indications 

 were estimated without difficulty to tenths of a degree. 



