PHYSICS. 127 



ever, it would be quite sufficient to carry a No. 4 copper 

 wire round the foundation of the house, up each of the cor- 

 ners and o-ables and alono; the ridges. If there are no me- 



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tallic connections with distant points, such as water and gas 

 pipes, it is not necessary to take any pains to facilitate the 

 escape of the electricity into the earth. 



Baxendell subsequently called attention to the fact that 

 the above system of protecting buildings from lightning was 

 suggested by the late Mr. Sturgeon in a paper read before 

 the London Electrical Society on March 7, 1838. Mr. Stur- 

 geon, moreover, advocated an efficient earth connection a 

 measure absolutely essential to prevent damage should the 

 building be struck by lightning. 



Fitzgerald has communicated to the Royal Society the 

 important fact that a ray of plane polarized light, when re- 

 flected from the polished pole of an electro-magnet, is not 

 simply rotated, as Kerr supposed, but emerges elliptically 

 polarized. To account for this result, he supposes differences 

 of density of iron in different directions due to the magnet- 

 ization ; whence two circular rays of unequal indices, which 

 by their combination produce, of course, an elliptic ray. 



Gordon has repeated with care the experiments of Kerr 

 on the effect of electric charge in causing double refraction 



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in glass, and has been entirely unable to produce the results, 

 though the means employed were as powerful and as delicate 

 as the latter's. 



Lodge presented to the Glasgow meeting of the British 

 Association an ingenious mechanical apparatus for illustrat- 

 ing many electric phenomena, such as the passage of elec- 

 tricity through metals, electrolytes, and dielectrics. In the 

 apparatus the current is represented by an inelastic endless 

 cord, the electro-motive force by a weight tending to urge 

 the cord forward. Resistance is shown by buttons moving 

 on the cord with friction, attached by strings more or less 

 elastic to the supports, by means of which counter-electro- 

 motive force is represented. 



6. Electric Light. 



Gauduin and Gramme have experimented to determine 

 the effect of the introduction of various more or less diffi- 

 cultly fusible substances into the carbons employed for the 



