VT3I,. LIV.] PHILOSOPHICAL TRANSACTIONS. 129 



object, I should recommend a circular building; in the periphery of which should 

 be placed storehouses sufficient in their number and extent to contain the quan- 

 tity of powder proposed. In the centre of this circle should be a well, very near 

 which should be erected a pole or mast, high enough to reach some feet above 

 the buildings of the powder magazine, or the buildings in its neighbourhood. 

 From this mast there should rise a brass rod, 5 or 6 feet in length, an inch in 

 thickness, and ending in a point; and from this rod a wire of copper of a size 

 not less than that of a large goose quill, should be conveyed down the mast, and 

 terminate in the water of the well. If there is no well, the wire should be laid 

 into the nearest water ; as the expence even of some hundred yards of a wire of 

 this sort can hardly be considered as an object in an affair of this importance. 

 For though there is reason to believe that the wire communicating with the 

 ground would prevent the mischiefs of a thunder-cloud, which came near an 

 apparatus of this sort; yet as water is a more ready conductor than the ground, 

 it should, if possible, be insisted on in this particular case, and employed. Mr. 

 West's apparatus, described by the before-mentioned Mr. Kinnersley, termi- 

 nated in an iron stake, driven 4 or 5 feet into the ground; yet the earth did not 

 conduct the lightning so fast but that, in a thunder-storm, the lightning was 

 seen to be diffused near the stake 2 or 3 yards over the pavement, though at 

 that time very wet with rain. It is presumed, that had this iron stake been 

 placed in water instead of earth, the lightning had not been visible, on account 

 of the water's receiving the electric matter more readily than earth. Where this 

 apparatus therefore is applied to powder magazines, it should certainly terminate 

 in water. At Mr. Hamilton's at Cobham, about 20 miles from hence, where 

 an apparatus of this sort was erected on a high and greatly exposed building, 

 as there was no water but at a great distance, the bottom of the wire was placed 

 deep in a hill of moist sand. If instead of one wire, two, three, or more, were 

 adapted to the brass rod in this manner, and conducted to the water, or if the 

 brass rod itself was continued to the water, I should consider it, in extraordinary 

 cases, as an additional security. This will explain my sentiments on the 3d, 4th, 

 and 6th questions. 



5. As the expectation of the utility of this apparatus is presumed to be the 

 preventing of the accumulation of electricity in its neighbourhood, by afixarding 

 a constant and easy passage to the electricity of the clouds surcharged with it, 

 nothing in my opinion need be apprehended from the apparatus electrifying the 

 air; as its principal operation is conceived to be the reverse of that, viz. divest- 

 ing the air of its electricity. I am well apprized from experiments made here, 

 that the earth is frequently electrified plus, and the clouds minus; and that this 

 change of plus and minus between the clouds and earth are sometimes seen to 

 vary several times in a quarter of an hour: but in that case it is presumed that 



"VOL. XII. S 



