XATUPxAL PHILOSOPHY. 143 



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done to a light-house in consequence of part of the discharge of lightning 

 having passed from the conductor to the lead fastenings of the stones. 

 The practical question for consideration was, how far they could safely run 

 lead between the stones of such a structure ; for if it were done partially, 

 leaving- a discontinuous series of such metallic fastenings, there would be 

 great danger of the stones being displaced by the, electric discharge. When 

 such fastenings are used, care should be taken that they are connected 

 together and with the earth by a continuous metallic conductor. Some 

 persons conceived that it is desirable to insulate the conductor from the wall 

 of a building by glass ; but all such contrivances are absurd, since the dis- 

 tance to which the metal could be removed from the wall by the interposed 

 insulator was altogether insignificant compared with the distance through 

 which the lightning must pass in a discharge from the clouds to the earth. 

 On being asked whether a flat strip of copper was not better than a cop- 

 per rod, Professor Farraday said that the shape of the conductor is imma- 

 terial, provided the substance and quality of the metal are the same. 



NOTICE OF SOME EXPERIMENTAL RESEARCHES INTO THE APPLI- 

 CATION OF THE VOLTAIC BATTERY TO THE IGNITION OF 

 GUNPOWDER. 



Capt. Ward having been requested by Sir John Burgoyne, Inspector- 

 General of Fortifications, to carry out some experiments for determining 

 the best form of voltaic battery for military purposes, he made himself 

 fully acquainted with the labors of Ohm, Wheatstone and others, and, 

 whilst verifying many of their theoretical researches, made them, the bases 

 for his own inquiries. After a most careful comparison of several bat- 

 teries, he adopted a Grove's Battery the solid elements being zinc and 

 platinum, and the liquid nitric acid and dilute sulphuric acid ; and he 

 finally ascertained that plates, only two inches square, were, perhaps, the 

 most satisfactory as regards work and cost. These he arranges in small 

 elementary batteries of six pairs, which, with the containing box, occupy 

 a space of only seven inches long, four inches wide, and four inches deep, 

 so that eight or nine of these elementary batteries, capable of igniting 

 gunpowder at the greatest distances likely to be required for military 

 purposes, would be arranged in a space of 1' 2" by 1' 4", or 1' 9' by 1' 

 4". In carrying out his experiments, and especially in determining the 

 relative value of each form of battery, and the effect of any modification. 

 of the battery or of the conducting wires in respect to the calorific effect, 

 Capt. Ward found that the deflection of the needle of the ordinay galva- 

 nometers was so great as to render it unfit for the estimation of differ- 

 ences in the electro -metric force in such powerful currents ; and he, 

 therefore, constructed a very simple instrument, by which he is enabled to 

 interpose one, two, cr more pieces of thin platinum wire in the circuit, 

 and, using this instrument, in conjunction with Prof. Wheatstone's Rheostat, 

 to determine the relative force of any battery, as well as the resistance of 



