514 



REPORT 18G7. 



those experiments. A large galvanic cell, consisting of cast iron and amal- 

 gamated zinc plunged in dilute sulphuric acid, was the source of electricity, 

 which was measured by a galvanometer with a coil of nine turns, 17 inches 

 in diameter. 



rr, L m I. Resistance of 



C3. C,. C,. Temperature Temperature ^^jj .^ ^^^.^^ 



of unit. 



of coil. 



of unit. 



o 

 tan 55 



tan 28 



62-65 



6-75 tan 28 18 tan 28 1-3 63-7 62-65 1-01901 



tan 59 32-5 tan 32 39-6 tan 32 22 59-24 58-39 1-01825 



The average resistance 1-01863 being reduced from the temperature 14"-5 

 Cent., at which the unit was adjusted, to 69°-9 Fahr., the average tempera- 

 ture of the calorimeter in the first series of experiments becomes 1-0191, 

 which, multiplied by 32808990, gives 33435640 as the resistance in British 

 absolute measure. 



A delicate thermometer was placed at a few inches distance from the 

 calorimeter, for the purpose of registering the temperature of the air. In 

 the Tables its indications are reduced to the scale of the instrument plunged 

 in the calorimeter. A string attached the handle of the stirrer to a stick, so 

 that the water could be effectually stirred without communicating the heat 

 of the hand. A wooden screen separated the observer from the apparatus. 



In the experiments of the first series a battery of five large DanieU's cells, 

 arranged in series, transmitted the current through the coil for 40' exactly 

 determined by chronometer. During this time twenty-eight observations of 

 deflection were obtained, seven at each end of the pointer directed N.E. and 

 S.W., and seven when it was directed N. W. and S.E. by reversing the current 

 in the galvanometer for the latter half of the time. The water was stirred 

 twenty-eight times. Its temperature was taken at the beginning, middle, 

 and end of an experiment. There were also fourteen observations of the 

 temperature of the air. 



Immediately after each experiment the horizontal intensity of magnetic 

 force was obtained by observing the deflection of the galvanometer and the 

 weighing of the current-meter produced by the same current. 



Before and after each experiment, two others were made in precisely the 

 same manner, but excepting the current, in order to discover the influence of 

 radiation and the conducting-power of the atmosphere. 



First Series of Thermal Experiments. 



