Intelligence and Miscellaneous Articles. 403 



bright-green rings appear at equal distances. On closer inspec- 

 tion, it is seen that from ring to ring a faint blue band stretches 

 above the red one in a wave-shaped form, corresponding to the up- 

 wards and downwards flickering of the upper part of the flame. The 

 greatest breadth of the blue band is in the neighbourhood of the 

 green rings. The sharpness with which the latter appear in the 

 mirror, indicates that the intervals of time during which the flame 

 emits intense green light are small as compared with the duration 

 of an entire pulsation. The beautiful green light does not arise from 

 the copper of the brass tube ; for it appears even in a glass burner ; 

 moreover spectral observation shows that the green of the hydro- 

 carbon spectrum is here concerned. 



3. The tube, in the condition suitable for'sounding the pipe, may 

 also be used for another experiment. If a platinum wire bent rect- 

 angularly be held vertically in the flame so that it is near the gauze, 

 the wire soon begins to be incandescent ; for the small flame is very 

 hot, and silver readily melts in it. If now the india-rubber gas-tube 

 be squeezed, the flame is extinguished and the wire ceases to ignite. 

 If after a few seconds gas be again admitted, the wire again begins 

 to glow without the gas being lighted. But when the wire is brightly 

 glowing, the rekindling of the flame can be effected by gently 

 breathing on it. If the flow of gas be increased, the cooling action 

 of the gas preponderates in the lower parts of the wire, the ignited 

 part ascends, but by diminishing the flow of gas can be depressed. 



Such a straight platinum wire, glowing after the flame has been 

 extinguished, might in many experiments serve as source of light, 

 provided care were taken to cut off currents of air. In the form of 

 a spiral, the wire would furnish a luminous source of heat, such as is 

 usually furnished by a spirit-lamp. Even flat platinum strips, 12 

 millims. in breadth, remain ignited for a length of several centimetres 

 after putting out the flame; cylindrically bent foil, of about 10 

 millims. diameter and 50 millims. height, suspended over the gauze, 

 would perhaps be better. With a spiral and with foil, the burner may 

 have a stronger current of gas. — Poggendorff's Annalen, January 

 1866. 



NOTE ON THE MECHANICAL EQUIVALENT OF LIGHT. 

 BY MOSES G. FARMER, ELECTRICAL ENGINEER. 



In the October Number of the Philosophical Magazine is copied 

 from Poggendorff's Annalen an article by Prof. J. Thomsen of Co- 

 penhagen, " On the Mechanical Equivalent of Light." 



His results show that about 13*1 foot-lbs. per minute represent the 

 mechanical equivalent of a spermaceti candle burning at the rate of 

 126^ grs. per hour. 



On the evening of the 4th of July, 1863, there was exhibited by 

 Mr. E. S. Ritchie, from the cupola of the State House in Boston, an 

 electrical light developed by the action of 250 Bunsen cells arranged 

 in five rows of nifty cells. 



The intensity of this light was estimated by Professor William 



