1872.] 



for Heat in Absolute Measure. 



91 



and it was necessary to make a careful thermometric comparison of the 

 temperatures of the junctions and galvanometer deflections. For this pur- 

 pose the junctions were tied to the bulbs of two previously compared 

 thermometers, having their stems divided to tenths of a degree Cent. ; 

 these were then placed in two vessels of water, one at the temperature of 

 the air, and the other heated by small additions of hot water, and kept 

 well stirred; simultaneous readings of the thermometers and galvano*. 

 meter deflections were then taken at various points of the scale*, from 

 which the formula 



i/=0°-0924 + 0°-00C0227# 

 was obtained, where y is the value of a scale-division in terms of a degree 

 Centigrade, and oc the galvanometer deflection ; and the difference of tem- 

 perature of the junctions is therefore 



^=0°-0924^ + 0°-0000227^ 2 , 

 from which the numbers in col. II. of the following Tables were calculated. 



The method adopted in reducing the observations was this : — Each 

 single set of readings was arranged in a vertical column, and the whole 

 series placed side by side with corresponding numbers in the same hori- 

 zontal line ; the means of the horizontal lines were formed into a similar 

 column, and divided into groups, each consisting of four consecutive 

 numbers, and the means of these groups form the numbers in col. I. of 

 the Tables. 



Col. II. contains the differences of the temperatures of the junctions at 

 intervals of four minutes, corresponding to the mean deflections in col. I. 



Col. III. contains the common logarithms of the numbers in col. II. 



Col. IV. contains the differences of the successive numbers in col. III. 

 divided by 4. 



Col. V. is formed from col. IV., by multiplying by the Napierian 

 logarithm of 10, and is the rate at which the difference of temperature 

 varies per minute. 



Col. VI. shows the quantity of heat emitted from the ball in gramme- 

 water units per square centimetre per second per degree of difference of 

 temperatures, and is formed by multiplying the numbers in col. V. by 

 •009385f, a constant depending on the surface of the ball and its capacity 

 for heat. 



* These readings were plotted, and the curve drawn through the points agreed very 

 closely with a portion of a parabolic curve whose equation is 



?/ = 24-f 10-6*- -019* 2 , 

 # denoting the deflections of the galvanometer, and x the difference of temperature; y 



is a maximum when - r = ^^ =279°, and, the colder junction having been at 1G J Cent,, 



we get 295° as the neutral point of the specimens of copper and iron wires used — a very 

 close agreement with former observations, considering the great distance of the neutral 

 point from the temperature of the observations. 



t The surface of the ball was 50-20 sq. centimetres, nntl its capacity for heat 28 31 



*i 2 



