44 



NOTES TO BOOK XI. 



(A.) p. 19. As an important application of the doc- 

 trines of electricity, I may mention the contrivances em- 

 ployed to protect ships from the effects of lightning. The 

 use of conductors in such cases is attended with peculiar 

 difficulties. In 1780 the French began to turn their 

 attention to this subject, and LeRoi was sent to Brest and 

 the various sea-ports of France for that purpose. Chains 

 temporarily applied in the rigging had been previously 

 suggested, but he endeavoured to place, he says, such con- 

 ductors in ships as might be fixed and durable. He devised 

 certain long linked rods, which led from a point in the 

 mast-head along a part of the rigging, or in divided stages 

 along the masts, and were fixed to plates of metal in the 

 ship^s sides communicating with the sea. But these were 

 either unable to stand the working of the rigging, or 

 otherwise inconvenient, and were finally abandoned. See 

 Le Hoi's Memoir in the Hist. Acad. Sc. for 1790. 



The conductor commonly used in the English navy, till 

 recently, consisted of a flexible copper chain, tied, when 

 occasion required, to the mast-head, and reaching down 

 into the sea ; a contrivance recommended by Dr. Watson 

 in 1762. But notwithstanding this precaution, the ship- 

 ping suffered greatly from the effects of lightning. 



Mr. Snow Harris, whose electrical labours are noticed 

 in the text, proposed to the Admiralty, in 1820, a plan 

 which combined the conditions of ship - conductors, so 

 desirable, yet so difficult to secure: namely, that they 



