118 DOVE ON THE ELECTRICITY OF INDUCTION. 



which cylinder had the more powerful action. With different 

 species of iron the following series was obtained, with some ex- 

 ceptions, in the individual experimental series * : — 



Soft iron. 



Gray iron from the crucible furnace. 



Soft steel. 



Gray iron from the cupola furnace, with hot blast. 



White iron. 



Gray iron from the cupola furnace, with cold blast. 



White iron from the cupola furnace, with cold blast. 



Hard steel. 



16. The determination of the exact number of wires which 

 compensate the effects of a cylinder as regards sensation is, for 

 another reason, difficult. For every degree of power in the battery, 

 the number is smaller than that required for compensation in 

 the galvanometer ; but in the case of iveaker currents, when the 

 excess of the one over the other can no longer be felt as a shock, 

 it becomes perceptible M'hen the current is stronger. The latter 

 sensation remains likewise for a length of time with apparently 

 unchanged intensity^ so that no perceptible change is produced 

 by diminishing the number of wires. 



17. I have therefore endeavoured to determine in another 

 manner the physiological series for solid rods. If from two 

 cylinders acting in opposition to each other a shock is felt, as 

 the result of the one current being more powerful than the other, 

 in order to ascertain from w^hich rod the shock proceeded, we 

 have only to draw out one of the rods from its magnetizing spiral, 

 and whilst it is being drawn out, to break and close the circuit 

 successively by turning round a rheotome. If the weaker rod is 

 being removed, then the shocks become constantly more intense; 

 if, on the contrary, the more powerfully acting rod is the one 

 moved, the shocks become weaker until the I'od has been drawn 

 out a certain distance, when they cease altogether. If this di- 

 stance is exceeded, shocks from the opposite current are obtained, 

 which gradually increase in intensity, and the distance which a 

 rod is drawn out from its spiral thus becomes a means of quan- 



* It is hardly necessary to remark that the arrangement of such series is 

 only intended to direct attention to the fact, that shght differences in tlie na- 

 ture of cast ii-on and steel materially affect the inducing action of iron, and not 

 positively to determine by the name of a substance the position which it holds 

 in the series. A series of this kind would only be absolutely correct, if identi- 

 cal substances could be designated by tlie same name. 



