On the Great Magnetic Disturbance of August 1859. B15 



state of the nerve above described consists in secondary electromotor 

 power, that is, in a well-known physical phenomenon. The course 

 of the secondary current, which is downward or direct in the nerve that 

 has been traversed by the upward or inverse pile-current, explains, 

 according to the well-known laws of electro-physiology, the effects 

 produced by it on that nerve on the opening of the circuit. 



" The differences of electromotor power found in various points 

 of the electrolysed nerve, the prevalence of this power in the part of 

 the nerve near the positive electrode, very probably also the different 

 degree of this secondary electromotor power in the various strata 

 which compose the interior and the envelope of the nerve, are cir- 

 cumstances which seem to explain the secondary current which takes 

 place in the nerve at the opening of the circuit, and which is direct 

 and most intense in the nerve which has already been traversed by 

 the inverse current, most intense also in the vicinity of the positive 

 electrode. 



" In order, therefore, to explain the phenomena which accompany 

 the opening of a circuit, we must henceforth have recourse to the 

 fact of the development of secondary electromotor power in nerves 

 and the laws according to which it manifests itself." 



November 21, 1861. — Sir Benjamin Collins Brodie, Bart, President, 



in the Chair. 



The following communications were read : — 



" On some Varieties of Tannin ; and on Larixinic Acid, a cry- 

 stallizable principle found in the Bark of the Larch Tree (PinusLarix, 

 Linn.)." By John Stenhouse, LL.D., F.R.S., F.C.S. 



** On the Great Magnetic Disturbance of August 28 to September 

 7, 1859, as recorded by Photography at the Kew Observatory." By 

 Balfour Stewart, Esq., A.M. Received June 28, 1861. 



During the latter part of August, and the beginning of September, 

 1859, auroral displays of almost unprecedented magnificence were 

 observed very widely throughout our globe, accompanied (as is in- 

 variably the case) with excessive disturbances of the magnetic needle. 



The interest attached to these appearances is, if possible, enhanced 

 by the fact, that at the time of their occurrence a large spot might 

 have been seen on the disc of our luminary, a celestial phenomenon 

 which we have grounds for supposing to be intimately connected 

 with auroral exhibitions and magnetic storms. 



The auroral displays just mentioned were very attentively observed 

 throughout Europe, America, and Australia. In many places these 

 were of the most gorgeous character, and other places were visited 

 by this meteor where its appearance was an event of very rare occur- 

 rence. Even from as low a latitude as Cuba we have a description of 

 it by the Director of the Havannah Observatory, accompanied with 

 the remark that only four previous displays had been recorded in 

 the traditions of the island. In not a few instances telegraphic com- 

 munication was interrupted owing to the current produced in the 

 wires ; and in some cases this proved so powerful that it was used 

 instead of the ordinary current, the batteries being cut off and the 

 wires connected with the earth. The descriptions of this meteor, 



Y2 



