1 76 Report on the New Dioptric Light of the Isle of Mai/, 



however being in combination, chemically, with the metal. 

 This is going much further in the idea of association without 

 combination than I have done. 1 merely mention the fact for 

 the purpose of directing M. Schoenbein's attention to the con- 

 dition of the iron and steel plates in Nol)iii's experiments. 

 My own impression at present is, that Nobili's thin plates 

 consisted of peroxide of lead formed at the positive electrode 

 in the solution of acetate of lead used ; and that it is just pos- 

 sible some of the differences between his tints and those of 

 Newton may depend upon, and some of his conclusions be 

 affected by, the circumstance that peroxide of lead has a power- 

 ful specific action on light, and is even in moderately thin 

 plates deeply coloured. 



I trust that M. Schoenbein's perseverance will very shortly 

 produce that reward it so well merits, the true explication of 

 the cause of the peculiar state of iron. 



I am, my dear Sir, very truly yonrs, 



Royal Institution, Jan. 21, 1837. M. Faraday. 



T 



XXXVII. Report hy a Committee of the Royal Society (of 

 Edinburgh) regarding the New Dioptric Light of the Isle 

 of May,* 

 HE Committee of the Royal Society appointed to co- 

 operate with the Commissioners for Northern Lights, met 

 at Dunbar, on Wednesday, 2Gth October 1836. Present, 

 Right Hon. Lord Greenock, V.P.R.S.E.; Mr. Robison, 

 Sec. R.S.E.; Dr. Traill, Dr. Christison, Professor Forbes. 

 Present also, Mr. Alan Stevenson, on the part of the Com- 

 missioners. 



The Committee were requested to compare the new fixed 

 dioptric light on the Isle of May, thirteen miles distant, with 

 the old catoptric light, placed on a temporary erection near 

 it. From the first point of observation, near the town of 

 Dunbar, the Committee were unanimous in pronouncing the 

 great superiority of effect of the new light, which appeared 

 brighter than the old one in the ratio of not less thaii 4 or 5 

 to 1. But upon changing the position of the point of obser- 

 vation to the eastward, the difference became less marked, and 

 at a distance (from the first station) of about one and a half 

 miles was scarcely appreciable, though the new light appeared 

 whiter and somewhat better defined. The reason of this 

 prodigious inequality of the old light in different azimuths, 



* Communicated to the Committee of Northern Lights, 28th Octoher 

 1826, and to the Lond. and Edinb. Phil. Mag., by Prof. Forbes. 



