Intelligence and Miscellaneous Articles. 471 



THE IMPROVED INDUCTION COIL. 

 To the Editors of the Philosophical Magazine and Journal. 



128 Sloane Street, Chelsea, 

 Gentlemen, May 18, 1857. 



I regret that Dr. Noad's disinterested conduct to a stranger should 

 have induced Mr. Hearder to make such statements as those which 

 appeared in the Philosophical Magazine of this month. He there 

 intimates that Dr. Noad introduced the instrument of his friend 

 during a lecture given at the Polytechnic Institution, thereby doing 

 him (Mr. Hearder) a commercial injury. Now I had seen Dr. Noad 

 but once before that lecture was delivered, I could not therefore have 

 been honoured by his friendship ; and had I been so fortunate, would 

 it have been just to suppress my humble attempts at improvement 

 for the sake of Mr. Hearder's pecuniary advantage .' 



With regard to Mr. Hearder's claim to the honour of having 

 introduced the improved induction coil into this country, I may state 

 that the coil which was exhibited at the Polytechnic Institution on 

 the 29th of September, was commenced in January and finished in 

 March 1856. This is not of much importance; and I should not 

 have named it, had it not been stated that I had constructed my coil 

 but a few weeks antecedent to the day of the lecture ; for it appears 

 to me that the individual who first makes an improvement jmblic 

 ought to have some slight share of the credit for such improvement, 

 although there may be others working in the same field with him. 



I fear that if Dr. Whitehouse comes forward as a claimant for the 

 honour of improving the induction coil, we shall be poorly off; for he 

 has not only improved that instrument, but practically applied it to 

 telegraphic purposes, thereby rendering it of high commercial im- 

 portance. 



I am. Gentlemen, 



Yours obediently, 



C. A. Bentley. 



ON THE ABSORPTION OF LIGHT IN TRAVERSING COMETS. 

 BY M. BABINET. 



I have endeavoured by every means which can be furnished by 

 optics, to ascertain the probable mass and density of comets. Ac- 

 cording to the estimates of Sir John Herschel, of Bessel, Struve, 

 Admiral Smyth, nnd even of Arago, the contrast of intensities has 

 given me as the atmospheric equivalent of a comet a number so small, 

 that it reduces to almost nothing the mass and the density of these 

 stars, which are not even gaseous, as is proved by the exact measure- 

 ments of Struve and Bessel, who were unable to detect any refrac- 

 tion in the nucleus of comets. 



It will be easily supposed that the absorption of light in traversing 

 material media was not the last optical notion to which I had recourse 

 in order to investigate the very exceptional nature of these moveable 

 masses of nebulous substance. But the result at which one arrives 

 is so exorbitant, that I should not have ventured to place it before 



