and on the Effects of Lightning on certain Shijos. 405 



evident that in this case its path was determined on the ge- 

 neral principles before laid down in sec. 17j p. 123. 



25. I shall now proceed to state a few cases of damage 

 to certain other ships of the navy, where metallic bodies 

 happened to be so disposed about the rigging and hull, as 

 to approximate in some measure to the conditions of ex- 

 periment 2, sec. J 7, and consequently to that perfect state 

 of defence against the expansive force of the electrical dis- 

 charge in which a ship would become placed, by perfecting 

 the conducting power of the masts, and uniting them into 

 one general continuous system with the metallic masses in 

 the hull, and with the sea. 



These cases are particularly interesting, and conclusive of 

 the general question of the protection to be afforded by such 

 a system. 



No. 1. — In September 1833, H.M. ship Hyacinth had 

 both the fore and main-top masts and top-gallant masts de- 

 stroyed by lightning in the Indian Ocean. The electric fluid 

 shivered these masts from the truck to the heel of the top- 

 mast, as indicated by the waving black line a b in the an- 

 nexed diagram, fig. 1, which represents the effects on the 

 main mast ; at the point h, it became assisted by the chain 

 topsail sheet leading to the deck at c, and so did no further 

 damage to the mast ; at d it received further assistance from 

 the copper pipe of Hearle's patent pump, leading to a small 

 well at e, and thence by a second pipe through the ship's side 

 under water, and by this passed safely into the sea*. 



26. Now it is evident here that a heavy discharge of light- 

 ning which shivered completely a sloop of war's main-top mast 

 and top-gallant mast varying from 1 1 inches to a foot in dia- 

 meter through a length of at least 80 feet, was conducted with- 

 out damage or fusion by an iron chain and a short copper pipe. 

 It is therefore important to state the dimensions of these me- 

 tallic bodies. Now the iron chain consisted of links 2\ inches 

 long, made of iron rod ~ inch in diameter. It reached from 

 the lower yard to the deck, a distance of about 50 feet. 



The pump consisted of copper pipe 4- pounds to the square 

 foot; it was 3 inches in diameter, and about the yyth of an 

 inch thick, extending through a distance of about 10 feet. 



The effects on the foremast were very similar, they are 

 omitted therefore for the sake of brevity. 



27. It is not a little remarkable, that five years after this, in 

 1838, this same ship was again struck by lightning, whilst at 



* These circumstances are minutely detailed by Capt. Blackwood, who 

 commanded the ship at the time, and may be seen in his interesting letter 

 on the subject, in the Nautical Magazine, vol. viii.,p, 116. 



