On the Lead-Zinc and Bismuth-zinc Alloys. 317 



Now Mr. C. V. Walker, in a paper communicated to the Roya* 

 Society (January 3 1 st, 1861), shows that the earth-currents which 

 accompany auroras are of very short period (say a few minutes), and 

 the auroras themselves also appear to be of a very fitful nature. AVe 

 cannot, therefore, well imagine how any combination of auroras and 

 earth-currents could cause the period of seven hours, which the 

 magnetic curves exhibit ; while at the same time we cannot fail to 

 associate the rapidly reversed earth-currents with those serrated 

 appearances which the curves present. 



The author suggests the following explanation of these pheno- 

 mena. The earth itself may be likened to the soft iron core of a 

 Ruhxnkorff's machine, and the lower strata of the atmosphere to an 

 insulating material interposed between the earth and the upper strata 

 of the atmosphere, which, being very rare, become conducting, and 

 form as it were the secondary coil of this arrangement. 



Now suppose a primary current, probably in our luminary, to in- 

 fluence the earth, and suppose its general direction to remain the 

 same for at least seven hours. This current would act on the 

 magnetic matter of the earth in the same manner during these seven 

 hours ; and would, therefore, account for the magnetic wave of seven 

 hours' duration. 



But although this current has been supposed to remain in the 

 same direction for seven hours, yet we may suppose that its inten- 

 sity, especially if it have an atmospheric origin, is of a fluctuating 

 character. Now any sudden increase or diminution in the intensity 

 of this current, heightened by the iron core on which it acts, i.e. the 

 earth, will produce secondary currents, 



1st. Along the surface of the earth, which is sufficiently con- 

 ducting for this purpose. 



2ndly. Along the upper strata of the atmosphere, which are also 

 sufficiently conducting. . 



These will be the earth-currents and auroras which, according to 

 this hypothesis, are therefore due to the fluctuating nature of this 

 primary current ; while, on the other hand, the magnetic disturbances 

 are due to its absolute intensity. 



"On the Lead-Zinc and Bismuth-Zinc Alloys." By A. Mat- 

 thiessen, F.R.S., and M. von Bose. Received August 28, 18G1. 



The fact that lead and zinc, and bismuth and zinc do not alloy 

 together in every proportion is well known, but there have been, we 

 believe, no determinations made as to the extent in which these metals 

 alloy with each other. 



The following experiments were made to ascertain quantitatively 

 what amount of zinc will dissolve in lead and bismuth, and, on the 

 other hand, the amount of bismuth and lead in zinc. 



The metals* were fused in a Hessian crucible over a 4-Bunsen 

 burner, stirred with a tobacco-pipe stem for a quarter of an hour, and 

 then allowed to remain quiet for half an hour in a fused state : during 

 the whole time a jet of gas was directed on the surface of the melted 

 metals. They were after this cast in a porous cell, which had been 

 previously heated to redness in a large crucible filled with sand. It 

 * Purified as described in the Phil. Trans. 1860, p. 177. 



