:(i^$ JAMAICA. 



•■•which c.)!iiiot 'oc doiie hy tlic miiTt? and yards themfcU'CS ; for thefc 

 from their heinlit, ilgurc, and confticiient parts, without ;ui apjia- 

 r.itii3 of this kiiu!, tend to direcl and condudt the lightning into the 

 ihip. .The application of fuch rods to the marts of fhips is neither 

 difficult nor expenfive.; as ^ brafs rod of 4 an inch thicknels may, 

 in mofl: caics, he large enough to anl'vver tliis purpofe. Era(s is 



/-preferable to iron in. hot climate?, as being lefs liable to mil; and 



' any metal, corroded witii ruft to tlie centre, ceafes to be of any life, 

 in dircvfting the I'ghtning, in the degree hoped tor from fuc!-i an ap- 

 paratus. 1 liave been informed by a gentleman, a native of Piiiladel- 

 phia, who had icon many of thefe apparatus fixed on houfes in that 

 province, that the iron conduclors ieldoin ruft: there; but, by 

 reafon of very frequent difcharges of the electric fluid through 

 them, they acquire a fine fleel-blue colour: and Mr. Franklin re- 

 lates, that in courfc of fome experiments for giving polarity to nee- 

 dles, were ihey fometimes finely blued, like a watcli Ipring, by 



rthe eledric flame, which was always the more permanently fixed, the 

 greater the diicharge that was fent through them. 



In Jamaica, iron is very fubje6t to rutt and fcale off; here, there- 

 fore, the rods had better be made of copper or brais, and painted or 

 gilt ; the coat of paint does not impede the deicent of the eledlric 

 matter through the metal, though a diicharge of this kind will per- 

 haps detach the paint, as was proved in an eleftrical experiment. In 

 other refpefts, iron or i\ee\ is the heft condudor, as being leaft apt to 

 fufe ; next copper; then brafs ; as in the following feries : 

 Degrees of expanfion by Mufchen-1 Iron. Steel. Copper. Brafs. 

 broeck's experiment ... J 80 85 89 no 



I fliall purfue Mr. Franklin's inftrudions in regard to the apparatus 

 proper for fecuring buildings, ftating at the fame time his general 

 theory on the operations of this fluid ; as his remarks are not only 

 curious but very ufeful, and neceflary for better underftanding this 

 fubjeft. 



Whatever properties we find in eletflricity, are alfo the properties 

 of lightning. This matter of lightning, or eledlricity, is an extremely 

 fubtile fluid, penetrating other bodies, and fubfifting in them equally 



-diffufed. 



When there happens to be a greater proportion of this fluid in one 

 body than in another, the body which has moft, will communicate 

 to that which has leaft, till the proportion becomes equal, provided 

 ihe diftance from them be not too great ; or, if too great, till there 

 be proper coududois to convey it from one to tlie other. 



If 



