﻿158 Intelligence and Miscellaneous Articles, 



2. DanielFs element (that is, copper, concentrated solution of 

 sulphate of copper, sulphuric acid, and zinc as above) 

 = 11*71 Siemens- Weber, 



3. Copper, sulphuric acid, zinc as above, 

 = 10-82 Siemens- Weber. 



The first electromotive force of the Grove's element was also de- 

 termined by Ohm's method, that is, by measuring two intensities, 

 different known resistances being inserted, in which the well-known 

 enfeeblement of the electromotive force by the current manifests 

 itself, although the intensities used only amounted to 1*7 and 0'9 

 Weber. 



In Ohm's method the errors which, when a long needle is used, 

 arise from the invalidity of the law of tangents are particularly pro- 

 minent. Hence it may be remarked that they may be avoided if 

 complementary angles to the two deflections of the needle are taken. 

 Combined with the rule for accuracy, that one current must have 

 about double the intensity of the other, it follows that it is most 

 advantageous to use angles of 35° and 55°, by which at the same 

 time the third condition of an accurate measurement is satisfied. 



The thermoelectric forces were throughout determined by the 

 method of compensation. By the aid of the electromotive force pre- 

 viously found for the Groves's element, and the great resistances 

 which could be used on the Siemens's scale, the reduction-factor of a 

 very delicate reflecting galvanometer was determined in Weber's unit. 

 A second galvanoscope with an astatic needle, as well as the Siemens's 

 scale, was used in the experiments to reduce the current in the ther- 

 moelement to zero. Siemens's standards of 1 to 4 units were inserted 

 in the circuit of the galvanometer. 



The resistance of the galvanometer itself was simply measured by 

 determining "the logarithmic decrement A of the oscillating needle 

 when the current was closed, and, further, the decrement X' after a 

 known resistance w f had been inserted in the circuit. Moreover the 

 logarithmic decrement X , with an open circuit, was known; for then 

 the desired resistance w of the multiplier is 



W=W f 5. 



The metals investigated were in hard-drawn wires of about 1 millim. 

 diameter. The copper was electrolytically deposited. 



The results are found in the following formulae ; for if one junc- 

 tion has a temperature of about 16° C, and the other one a tempe- 

 rature about t° higher, from the observations the electromotive force 

 e is found in Siemens- Weber units. 



German silver and copper. 

 e=0-0001549* + 0-000000291* 2 . 



Copper and iron. 

 e=0-0000969*+0-0000000149* 2 . 



German silver and iron. 

 e=0-0002476*-f-0-000000196* 2 . 



