76 Intelligence and Miscellaneous Articles. 



ON A NEW STANDARD OF LIGHT. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, New York, Dec. 4, 1879. 



In a recent Number of the Philosophical Magazine (Nov. 1879, 

 p. 392 &c.) Mr. Louis Schwendler communicates a memoir " On a 

 New Standard of Light." It consists of a strip of platinum raised to 

 a standard temperature by an electric current. He remarks of this 

 method, that it appeared to him so natural and simple that he could 

 scarcely understand why it had not been proposed and acted upon 

 before. Subsequently he found that Dr. Draper had suggested the 

 same previously. Mr. Schwendler's experiments were instituted 

 on behalf of the Board of Directors of the East Indian Railway 

 Company, under orders of the Secretary of State for India, to inquire 

 into the feasibility and practicability of lighting up Indian railway- 

 stations by the electric light. 



In view of this, will you do me the favour to reprint a passage in 

 the Philosophical Magazine. It is in the Number for May 1847, 

 in a memoir by me, " On the Production of Light by Heat," p. 359. 



" Among writers on Optics it has been a desideratum to obtain 

 an artificial light of standard brilliancy. The preceding experi- 

 ments furnish an easy means of supplying that want, and give us 

 what might be termed a unit lamp. A surface of platinum of 

 standard dimensions, raised to a standard temperature by a voltaic 

 current, will always emit a constant light. A strip of that metal, 

 1 inch long and -fa of an inch wide, connected with a lever by 

 which its expansion might be measured, would yield at 2000° a 

 light suitable for most purposes. Moreover it would be very easy 

 to form from it an available photometer, by screening portions of 

 the shining surface. An ingenious artist would have very little 

 difficulty, by taking advantage of the movements of the lever, in 

 makiug a self-acting apparatus in which the platinum should be 

 maintained at a uniform temperature notwithstanding any change 

 taking place in the voltaic currents." 



I am, Gentlemen, 



Tours respectfully, 



John W. Draper. 



ON THE PASSIVITY OF IRON. BY L. VARENNE. 



When a piece of iron is put into the ordinary commercial nitric 

 acid a reaction is immediately set up and becomes intensely vigorous. 

 Concentrated nitric acid, that which in the laboratory mostly bears 

 the name of fuming nitric acid, does not react upon iron ; moreover 

 the metal acquires, by contact with this acid, the singular property 

 of not being attacked by the dilute acid : the fuming acid is said to 



