446 PHILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



way of rocks ; but it is also incumbent on him, in avoiding the rock, not to 

 take so large a compass as to run his ship on a quicksand. When I say that 

 sharp-pointed conductors may in some cases diminish danger, I speak of them, 

 perhaps, rather too favourably : for their power of stealing away the electric 

 fluid being confined to cases where the accumulation is small, it follows, that 

 they only operate where their operation is not wanted. The cases against which 

 we wish principally to provide, are the explosions of extensive and highly elec- 

 trified clouds ; and here we have seen, that blunted ends, as acting to a much 

 smaller distance, are entitled to the preference. 



If it be admitted, that sharp-pointed conductors are attended with any, the 

 slightest degree of danger, how much must that danger be augmented by carry- 

 ing them high up into the air, by fixing them on every angle of a building, and 

 making them project in every direction ? Ought this to be advised while there is 

 still a doubt of the possibility of their doing mischief? And can the committee, 

 therefore, be perfectly justified for giving such a decided preference to the use of 

 sharp conductors, in defiance of numerous experiments, not one of which they 

 have attempted to controvert ? 



Lastly, I beg leave to correct an expression I have used with respect to 

 pointed conductors, that they only operate where their operation is not wanted. 

 Now this is not accurately true: for if by operating on a quantity of electricity 

 too small in itself to do mischief, they prevent its increasing to a great and 

 dangerous quantity, this would, as far as it goes, be a very considerable advan- 

 tage. I ought therefore to have said only, that pointed conductors afford no 

 protection where the danger is great and imminent, and only obviate that which 

 is distant and problematical ; and that these last are not the cases against which 

 we principally wish to provide. 



XXXVIII. On the Use of an Amalgam of Zinc, for the Purpose of Electrical 

 Excitation, &c. By Bryant Higgins, M. D. p. 86 1. 

 By divers experiments lately made by myself, and repeated by others, I find 

 that, agreeable to the suggestion made in my last course of chemistry, the amal- 

 gam of zinc, which contains 4 times more quicksilver than zinc, is much better 

 / for electrical excitation than the tin amalgam of tiie ingenious Mr. Canton, 



when used in the same circumstances. I also find, that electrical cylinders are 

 easily and effectually cleansed by applying to them a piece of the dry skin of the 

 dog-fish while the cylinders are turned round ; and that in this method of cleansing 

 the glass cylinders, we avoid the inconvenience of removing the cushion, and the 

 danger of scratching the glass, to both which we are exposed in the use of whiting 

 and other cleansing powders. 



