590 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



regulated distance. These vibrations are controlled by auto- 

 matic mechanism, and are made to follow each other so rap- 

 idly that the effect of the rapid succession of sparks is to the 

 eye a continuous light. 



At the time of this writing much interest is manifested at 

 the assertion that Mr. Edison has succeeded in effecting the 

 practical subdivision of the current, and that he has devised 

 a novel system of lighting, which, though no statement from 

 the inventor has yet appeared, is reputed to depend upon the 

 resistance interposed by platinum surfaces. 



Upon this point, it may be of interest to note that Messrs. 

 Houston and Thomson, who have carefully studied the ques- 

 tion of the economical production of light from electrical cur- 

 rents, have inferred that the employment of platinum, or sim- 

 ilar resistant substances, whose temperature of fusion and 

 vaporization is low as compared with that of carbon for the 

 production of light, must be far less economical than the use 

 of the arc itself. Until Mr. Edison's plans are made pub- 

 lic, however, it would be premature to pass judgment upon 

 them. 



The Sawyer-Mann electric lamp may finally be mentioned 

 as the latest American contribution to this important subject, 

 which is claimed to have overcome most, if not all, of the ob- 

 jections before advanced. The lamp employed by these in- 

 ventors is enclosed in a hermetically sealed tube of glass 

 filled with nitrogen-gas, a slender pencil of carbon complet- 

 ing the circuit between what would otherwise be the two 

 carbon poles. This rod, or pencil, becomes luminous through- 

 out its entire length, and by its incandescence furnishes the 

 light in place of the ordinary voltaic arc. The sealing of the 

 apparatus in an atmosphere of nitrogen is for the purpose of 

 preventing its burning away, which would speedily occur in 

 the air. An essential feature of the invention is said to be 

 "an ingenious device for dividing the current, and for main- 

 taining a constant resistance in the circuit, whether the lamps 

 are on or off." This invention is of so recent a date that no 

 record of its actual performance is at hand from which to 

 judge of its merits, though from the description it would ap- 

 pear to be very promising. The device of using a continu- 

 ous rod of carbon placed in an atmosphere which is a non- 

 supporter of combustion is not a new one, having been em- 



