Mr. Snow Harris ott Lightning Conductors. 461 



'sin 7M /3\^ /sin m yv^ sin?w/3sinwy "I 



{m a.)'^ {_\ m ^ .' ^ my ' m (S niy^ j 

 or by 



S^ r ,sinwy\^ . (smmu\^ ^smmy sinmct ^"1 



(»z^)^(^V7«y/ ^ m a. * my ma, J 

 or by 



S^ f/sinwzax'^ tsmmBs^ ^^mma. smmB "1 



/ ToS ( ) + ( a ) -- 2 ■—- cos 7« y y. 



{myY \_^ m a. I ^ mp ' ma. m^ 'J 



The sura of the squares of the coefficients of sin 4> and 

 cos <p may be put in another form. 



{/3 (1 — cos 2 m y) - y (1 — cos 2 w /S)}^ 



+ {yS sin 2 w y — y sin 2 7» /3}^ 



= 2/3H 2 y2-2/Sy-2/8 y cos 27w(y-/S) + 2(/3y-y^)cos 2 w/3 



+ 2 [^y — ^) cos 2 wy 



= 4f ^y (sin w a)^ + 4 y a (sin w ^f 



+ 4 « /3 (sin w y)^ 



Hence the intensity of the light at M 

 __ S^ f {sin muY^ {s'lnm^f (sin my)°l 



""w«.Wy8.Wy\ 7«a w/3 wy j' 



y being that projection which is equal to the sum of the other 

 two. 



St. John's College, Nov. 2, 1839. 



LXXI. On Lightnifig Conductors, and on certain Pri7iciples 

 ill Electrical Science ; beijig an investigation of Mr. Stur- 

 geon^s Experime7ital and Theoretical Researches in Electri- 

 city, i^iMished by him in the '■^ Annals of Electricity^^ SfC. 

 By W. Snow Harris, Esq., F.R.S. 

 (Illustrated by Plate II.) 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



1 N the Annals of Electricity for October last, will be found 

 ■■■ a memoir on Marine Lightning Conductors. This memoir 

 is addressed to the British Association, and is considered by 

 Mr. Sturgeon, the author of it, to merit in a high degree the 

 especial consideration of all the learned scientific bodies in 

 Europe and America. 



The author endeavours to show, that a metallic rod whilst 

 transmitting a charge of electricity, is always productive of 



