XVII. A letter to Dr. Benjamin Franklin, F. R. S. giving an account of the appearance of lightning on a conductor fixed from the summit of the mainmast of a ship, down to the water: By Capt. J. L. Winn [ *88 ] Received February i , 177a, XVII. A Letter to Dr. Benjamin Franklin,. F. R* S* giving an Account of the Ap­ pearance of Lightning on a fixed from the Summit of the Mainmafi of a down to the Water; By Capt. J. L. Winn. S I R , Read March 2 9 , ~WT is a com m on, and, I am afraid, juft;. J [ com plaint, that Teamen are exceed­ ingly backw ard in availing themfelves o f tho^dif- coveries w hich men of fcience have m ade, and the directions w hich they have given for their benefit • and fafety. N otw ithftanding the pains feveral em i­ nent philofophers have taken, to bring conductors into general ufe, as well in (hips as h o u fes; ; it is too true that very few veffels are furniihed w ith them* though fcarce a year pafles, that does not afford us- inftances (fome o f th e m terrible ones), o f ihips b ein g | ftruck by lig h ten in g : for my part, l am never w ith? out a conductor in my (hip. I have h ad them o f various conftruCtions:: that w hich I. now ufe, is a chain o f copper wire, as deferibed in th e annexed p la te .^ T h a tfu c h a chainyfo difpofed,m ay conduCtthe- lightening, and prevent a firoke th at m ight deffroy a ftlip, has: often been dem onftrated^ but a circum - * . ftanee. D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 Voi.LX.TkB.VJI.Pa D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 fiance that occurred in my Jaft voyage, may perhaps have greater w eight w ith Tome feamen, than all the reafonings o f the electricians• I f it fhould be a means o f perfuading them to m ake ufe o f conductors, my intention will be anfwered. In April lafty . as we approached the coaft o f America, we met w ith ftrong South-rwefterly gales: : they had continued feveral days, w hen exceeding dark v heavy clouds arofe in th e oppofite quarter, forced againft the wind that blew > w ith; ms, till they had covered all th e N o rth -e a fte rn h a lfo f the hem ifphere: the itruggle then between the tw o winds was very extraordinary; fometimes one prevailing, fometimes the other. . I w asapprehenfive w e fliould have m uch lightning, and got ,my conductor in order $ w hen, in i hauling u p ,th e mainfail, the fheet block (truck vio­ lently againft the b a c k p a y s , to w hich the chain was ; fattened ( E E in fig* i . T ab. V II.), and, as I found 1 afterwards, broke the latter, which occafioned th e phenom enon I am going to defcribe.. It: was .near r m idnight and very dark, when I firft obferve a pale bluifh light a few feet above the quarter ra il: at firil t I thought it proceeded from the light in the binnacle; • but,finding that it frequently disappeared and return­ ed again precifely in the fame place, and that it fome- • times emitted fparks not unlike thofe o f a fmall fquib, ; I began to fufpeCt that it proceeded from the con­ ductor. T o be certain, I ordered all the lights to be put out below, and, that no raya o f light m ight iflue fropi the binnacle, I covered it entirely with my cloak. I .$ was prefently confirm ed,in my conjecture, th a t the lio-ht. and fparks which I had obferved proceeded ; fcom the chain 5 for, placing myfelf near it, during D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 [ I 9 ° ] 't h e fpace o f two hours and a half, I faw it frequent­ ly em it continued ttreams o f rays or fparks (fee % • '4*)/ fo re tim e s fmgie drops as it were flowlv fucceeding to each other, and fometimes only a pale feeble light. On examining next morning, I found •the chain broken at B, h a lf the eye o f each link being quite gone, and the points ot the remaining halves about three fourths o f an inch afu n d er: luckily* the chain was fattened to a fm a lle r rope ( % above and below the eye o f each link, w hich pre­ vented that part o f the chain below B, from falfino* into the water, or o f being feparated from the part ;above B, beyond th e ttriking or attra&ing diftance, I am with the greateft refped, S i r , Y our obliged hum ble fervant, J . L . W in n . References D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 I *9* } References to Plate V I I . , A A A T h e conductor, a chain o f copper wire, o f th e thicknefs of the barrel o f a fmall