112 DOVE ON THE ELECTRICITY OF INDUCTION, 



the resulting current is only produced by the inserted iron, as 

 the direct action of the connecting wire upon the secondary wire 

 is completely compensated. 



The galvanic batteries used in the experiments were some- 

 times small calorimotors of two coils and 4 inches high, at other 

 times larger many-celled troughs united to form one battery 13 

 inches in width, with four interposed copper and amalgamated 

 zinc plates. Afterwards constant batteries were employed with 

 advantage, either Bunsen's carbo-zinc battery, or Grove's pla- 

 tino-zinc battery. The experiments with thermo-electricity were 

 made with a thermo-battery consisting of eight bars of antimony 

 and bismuth, w hich formed at their upper and lower extremity a 

 chess-board of sixteen squares, each 8 hues in width, whilst the 

 height of the bars was 3 inches 8 lines. The poles of this bat- 

 tery, which terminated in wide vessels containing mercury, 

 were connected by the magnetizing spirals, and the unequal 

 temperatures were produced by water cooled to 0° Celsius by 

 means of snow, and by a suspended plate of red-hot iron. Af- 

 terwards a simple thermo-battery was used consisting of two 

 bars of bismuth and antimony, 3" f" in length and having a 

 square section of 8'" 5, soldered together, and warmed at the part 

 where they were soldered by the flame of a spirit-lamp. All the 

 connexions of the thick wires were made by means of cylindri- 

 cal vessels containing mercury, with holes bored through them. 

 All the connexions of the thin wires were effected by clamps 

 doubly bored, the holes being at right angles to each other*. 



3. Differential Inductor for magneto-electricity. 



7. When the primary current was that of a Saxton's machine, 

 instead of the inner spirals of thick copper wire, two spirals of 

 thin wire ^"' thick and 400' in length were used, each an inch 

 wide and a foot long. The outer spirals were the same as those 

 used in the former differential inductor. 



4. Differential Inductor for frictional electricity. 



8. Upon two strong cylindrical glass tubes one foot long and 



* If the holes in the clamps are at right angles to each other, by means of 

 one screw the crossed wires can be clamped together. The holes being bored 

 completely through the clamps, admit of the wires being connected not only at 

 their ends, but by drawing any one of the wires the requisite distance through 

 the clamp, the end of. the one wire can be connected with the middle of the 

 other. 



