272 The Rev. S. Haughton on the Chemical Composition of 



ignited was constantly passing through the coil of the galvano- 

 meter. I forgot to observe the deflection produced by the voltaic 

 current during the combustion of the metals ; but during the 

 ignition of the coke-points, the deflection was frequently 

 observed : the average deflection did not exceed 40°. I have 

 since found that the current from a single pair of plates, each an 

 inch and a half square, produces a deflection of 58°, which 

 requires a current about twice as powerful as one which would 

 cause a deflection of 40°. Hence not more than about the T J gth of 

 the power of the 70 4-inch cells was employed in producing the 

 coke light. Fifteen-sixteenths of their power was inactive, whilst 

 the exciting fluid was acting on the metals, and wasting its own 

 strength. Hence it strikes me, that for the electric light which 

 is now used for practical purposes, a battery consisting of 80 or 

 90 cells, each about an inch and a half or two inches square, 

 would be the most (Economical. I purpose to get a battery of 

 100 pairs of plates, each two inches or an inch and a half square, 

 in order to try its power of producing the electric light. 



The greatest length of the flame between the coke-points 

 appeared to me to be less than it would be with a nitric acid 

 battery of 70 4-inch cells. Hence I infer that the intensity of 

 the single fluid battery is less than that of the nitric acid battery, 

 although the quantity of electricity is much greater. The state 

 of some of the cells after the experiments, excited an apprehen- 

 sion that the distance of ygth of an inch between the zinc and 

 iron may not be sufficient for the free descent of the sulphate of 

 zinc, though it may permit the hydrogen to escape with perfect 

 freedom. However, I am inclined to ascribe the condition of 

 the cells, which were new, to the sand which remained attached 

 to them after they were taken out of the mould. 



Maynooth College, 

 March 15, 1855. 



XLI. Notes on Mineralogy. — No. I. On the Chemical Compo- 

 sition and Optical Properties of the Mica of the Dublin, Wick- 

 low, and Carlow Granites. By the Rev. Samuel Haughton, 

 M.A., Professor of Geology in the University of Dublin*. 



THE minerals included in the mica family may be divided 

 into various groups, founded on their chemical composi- 

 tion and optical properties. 



Chemically considered, they are divided by Rammelsberg and 

 others into three families : — 



* Communicated by the Author. 



