130 ANNUAL OF SCIENTIFIC DISCOVERY. 



ried. He explains the whole by supposing that the molten lead, 

 at the temperature to which it is raised by the contact with liquid 

 iron, forms an incipient vapor of lead, which is prevented from 

 escaping by the skin of solidifying metal which forms on the top. 

 The lead vapor, according to this explanation, keeps the lead rest- 

 ing upon the surface of the iron. It seems that in large quantities 

 the result is different, since it is known that lead is occasionally 

 tapped from the bottom of blast furnaces, which smelt certain 

 classes of ores containing lead, and in these cases the lead is 

 found below the liquid iron, according to its greater specific 

 gravity. Engineering. 



SPEED OF MECHANICAL FORCE. 



If a continuous solid iron rail was laid along a track for a dis- 

 tance of 150 miles, no amount of force applied at one end could 

 move the other in less than one minute and a quarter, the time re- 

 quired for mechanical force to travel in iron that distance. 



COLOR OF SUNLIGHT. 



M. Brucke has observed that diffused solar light, instead of 

 being perfectly white, is tinged with red. The light of burning 

 magnesium, which appears to be so like sunlight, has a tinge of 

 violet.. 



PHOTOMETRIC APPARATUS. 



M. Paul Berard, who directs, with M. Paul Andouin, the "Labor- 

 atory of Essay for the Illuminating Power of Gas," established in 

 Paris, under the head direction of MM. Dumas and Regnault, 

 has confirmed by many experiments results obtained, having a 

 double view. 1. Two flames of equal density being given, one 

 produced by a carcel lamp burning under fixed conditions, the 

 other by a gas-burner, burning as much as possible under the 

 same conditions, to determine the respective consumptions of oil 

 and gas, in a given time, for each of the apparatus. 2. To study 

 different burners, and the best conditions for the combustion of 

 the gas. 



The first problem was completely resolved by a series of pho- 

 tometric apparatus, very well constructed by M. Deleuil, and 

 which comprise a carcel lamp burning at the normal rate of oil, 

 a Foucault photometer with starched glass plates, and a telescope 

 and movable plates, a standard burner and an argand one with 

 80 holes, and an automatic balance indicating by a scale, with the 

 precision of 1 centigr., for a charge of 3 kilos, the quantity burned 

 by a carcel lamp. M. Audouin said nothing of the photometric 

 method ; he did not even mention the name of M. Deleuil, but he 

 enumerated very rapidly the conclusions of the experiments on 

 burners. Let us mention them, as they are truly well defined. 

 With bafs-wing burners the maximum of illuminating power cor- 

 responds to a slit seven-tenths of a millimetre wide. The same 

 quantity of gas can give, when it burns in a good burner, four 



