60 



REPOllT — 1876. 



deal of the effect duo to temperature oscillations already referred to. lu one 

 experiment in particular in wliicli a Grove's batter}^ was used, with alterna- 

 tions at the rate of only thirty per second, this effect came out very strong, 

 the spot swinging off the scale when the smaller battery was reversed. 



Without dwelling on these, I proceed to give the results of the final set of 

 experiments, which were in every way by far the most satisfactory. 



In the three following experiments the Daniells were used as before ; the 

 alternations were made by means of the tuning-forks at the rate of GO per 

 second. Three wires were experimented on, a platinum, a German-silver, 

 and an iron wire. The balancing resistance was the German-silver bobbin 

 with small resistance-box, which was on the left, except in the second experi- 

 ment, where it Avas on the right. The electromotive force between D and F 

 was now found directly by the electrometer ; as a control the sensibilities 

 are given as well. New spade-pointed platinum dippers were used, and 

 answered admirably during the whole time the experiments were going on. 



In the last set of experiments a higher electromotive force was used, viz. 

 four cells of Grove and two, every thing else being as before. The same three 

 wires were experimented upon, but with perfect success in the case of the iron 

 wire only. In the experiments on the other two, although the electrometer 

 readings were very stead}' and satisfactory, yet a steady balance could not 



be obtained ; stiU it could be seen that the -1- -1- and -| balances did not 



differ by much; it seemed that there was, in the case of the German-silver 

 wire, a tending towards the effect so often alluded to. 



The following is the experiment with the iron v,-irc : — 



Using the additional data that the resistance of the metre of platinum- 



iridium wire on the bridge is "075 ohm, and that Latimer Clark's Standard 



Cell (1'457 volt) produces a deflection on the electrometer used of about 320 



divisions, we get roughly the following results {e denotes the electromotive 



* Electrometer deflection for Latimer Clark's Standard = 320. 



