64 Royal Society : — 



takes place, we find that with the lead and tin alloys it generally 

 requires twice as many volumes of the former as of the latter to 

 reduce a metal of class B to a certain conducting power. 



3. That the turning-points of these curves are not chemical com- 

 binations we may assume from the fact that they only contain very 

 small per-centages of the one metal. 



4. That the alloys at the turning-points have their calculated 

 specific gravities. 



5. From the similarity of the curves of the conducting power of 

 alloys, where we may assume we have only a solution of one metal 

 in the other, we may always draw approximatively the curve of the 

 alloys of any two metals if we know to which class they belong. 



B. That some alloys are chemical combinations ; for — 



1. At the turning-points of the curve we generally find contraction 

 or expansion. 



2. We have no regular form of curve, so that we cannot a priori 

 approximatively draw it. 



3. At the turning-points of the curve, the alloy retains large per- 

 centages of each metal. 



4. The appearance (crystalline form, &c.) of the alloys at these 

 points is different from each other. 



C. That some alloys are only mechanical mixtures ; for example, 

 bismuth-zinc, lead-zinc, some silver- copper alloys, &c. 



The question now arises, To what is the rapid decrement of the 

 conducting power of the metals belonging to class B, when alloyed 

 with other metals, due 1 



The only answer I can at present give to this question is, that 

 most of their other physical properties are altered in a like manner ; 

 for where we find no marked change in most of the physical pro- 

 perties, as in group I, and in the second group on the one side of 

 the curve, then we have nearly their calculated conducting powers. 



In the Appendix I have given some determinations of the con- 

 ducting power of pure gold, which I find has a higher value than 

 that generally quoted. 



In conclusion, I may take this opportunity of thanking Dr. M. 

 Holzmann for the excellent manner in which he has carried out the 

 greater part of the experiments. 



" On an extended Form of the Index Symbol in the Calculus of 

 Operations." By William Spottiswoode, Esq., M.A., F.R.S. 



" Problem on the Divisibility of Numbers." By Francis Ele- 

 fanti, Esq. 



" On the Structure of the Chorda Dorsalis of the Plagiostomes and 

 some other fishes, and on the relation of its proper Sheath to the 

 development of the Vertebrae." By Professor Albert Kolliker. 



" Remarks on the late Storms of October 25-26 and November 1, 

 1859." By Rear- Admiral FitzRoy, F.R.S. 



As many of our Society must doubtless be interested in the nature 

 and character of that storm in which the * Royal Charter ' went to 



