xlvi Introduction to the Makerstoun Observations, 1844. 



64. The observations from which this result was obtained were very good, con- 

 sidering that the whole angle of deflection was less than 3°, and it may therefore be 

 worth examining the individual results for the highest and lowest temperature. The 

 whole number of results was 15, the mean difference, from the final result given 

 above, =0-000025, and the probable error of a single result was therefore about 

 0-000021. 



The mean of 9 results for the mean temperature 49°"7 gave q = 0-000289 

 The mean of 6 68°-7 q = 0-000286 



so that the temperature coefficient for this bar is constant within the ordinary tem- 

 peratures occurring during the observations in which it was employed. 



Bijilar Magnet. 



65. The temperature coefficient for this magnet was also determined by means 

 of hot and cold water experiments, Nov. 9 and 10, 1843. See page xli., Introduc- 

 tion, 1841-2, for the details. The whole number of results was 30 : the mean gave 



The correction for 1° Fahr., Q = 0000294. 



66. If the 27th and 28th,results (counting from the top of the last column of 

 Table 19, p. xli., Introduction, 1841-2) be rejected, as it is believed that the great 

 difference of both from the mean was probably due to one error in reading, we find 

 the average difference of the 28 results from the mean = 0*000021, and the probable 

 error of a single result was therefore about 0-000017. Combining the results from 

 high temperatures together, and similarly for those from low temperatures, we find 



The mean of 15 results for the mean temperature 48 o, gave Q = 0-000292 

 The mean of 13 68°7 Q = 0-000295 



so that for the bifilar magnet, also, the temperature coefficient is constant within the 

 ordinary temperatures of 32° to 80° Fahr. 



67. The correction for the expansion of the silver wires and brass grooved 

 wheel, =0*000010, being added to the value of Q above, we have 



The temperature correction for 1° Fahr., from hot and cold water experiments, q = 0-000304. 



68. As the observations in connection with the balance needle had shewn that 

 there might exist variations due to temperature, other than those due to the varia- 

 tion of the magnetic moment of the magnet, such as the varying elasticity of the 

 suspending wire of the bifilar magnet, the temperature coefficient was determined 

 in the following manner, which had at first been found to give consistent results for 

 the balance needle. 



