Mr. R. S. BroLigh on a Case of LiyJitnlng. 105 



meiits. This expectation has been so far fulfilled that I think 

 a short account of the experiments may not be uninteresting to 

 your readers. 



The magnet consisted of a bar of soft iron 2 feet 2 inches 

 long and 2^ inches in diameter, on which were two helices 

 containing each about 1030 turns of wire. It was excited by 

 ten quart Grove cells arranged in series. The submagnet 

 consisted of a wedge of soft iron 5 inches long by 2 inches 

 thick at the wide end, and having an edge 2^ inches long. 



The magnet being placed horizontally, the submagnet was 

 brought up against its polished end, but prevented from touch- 

 ing it by two pieces of copper "bell "-wire. The light of a 

 paraffin-lamp was polarized by a large Nicoi's prism and 

 allowed to fall on the pole at about 45°. The reflected light 

 was examined by the Jellett analyzer described by me in the 

 Philosophical Transactions for 1877, part 1. The effect was 

 most marked and distinct. 



The following readings of the plane of polarization were 

 taken : — 



Current direct, 



271 55 

 271 57 



Current reversed. 



271 30 

 271 27 



271 54 

 271 52 



Mean double rotation 



271 28 

 271 26 



... 26' 45'' 



I have not as yet been able to get any distinct effect with- 

 out the submagnet. Until this can be done, " absolute" mea- 

 sures of the amount of rotation due to a given strength of pole 

 will not be possible. 



J. E. H. Gordon. 



Pixholme, Dorking. 



XIV. On a Case of Lightning ; with an Evaluation of the Po^ 

 tential and Quantity of the Discharge in Absolute Measure, 

 By R. S. Bkough*. 



THE south-west monsoon of 1871 may be considered to have 

 been characterized in the neighbourhood of Calcutta no 

 less by its copious and protracted rainfall than by the violence 

 and frequency of its thunderstorms. During the progress of 



* Communicated by the Author, having leen read before the Asiatic 

 Society of Bengal on the ?th of February, 1877. 



