54 A. 3£ Mayer — Physical Properties of Vulcanite. 



in azimuth 90°, 10*6 candles; in azimuth. 0°, 6'6 candles of 

 light ; that is the edge of the flame gives about 38 per cent 

 less light than that given by the side. The flame of the Hitch- 

 cock lamp and the flame of the ordinary petroleum lamp with 

 chimney increase in candle power with the azimuth in different 

 rates. The reason of this is that the glass chimney acts as a 

 reflector and tends to equalize the illumination in different 

 azimuths. The photometric curve of the Hitchcock flame 

 cuts the circle of average illumination at 26f° ; the curve of 

 the ordinary petroleum flame cuts its circle of average illumi- 

 nation at 30° of azimuth. A flat coal gas flame does not (to 

 me) show any difference in candle power, when its edge or flat 

 side is presented to the ordinary Bunsen photometer. 



As to the cause of the absorption of light, or, of the opacity 

 to light of a petroleum flame I have no hypothesis to offer ; 

 nor have any of the experiments I have made on the absorp- 

 tion action of this flame given me any clue as to its cause. 

 As a friend observed, all we can say is that the gas house does 

 for the gas of the coal gas flame what the lamp does not do for 

 the gas of its flame. 



Stevens Institute of Technology, Hoboken, N. J. 



Art. YIII. — On the Physical Properties of Hard-Rubber, 

 or Vulcanite y by Alfred M. Mayer. 



The discovery of the large coefficient of expansion of hard- 

 rubber by Kohlrausch,* in 1873, and of its remarkable diather- 

 mancy by Bell,f in 1880, attracted the attention of physicists 

 to this substance. In this paper I give additional and more 

 minute experiments on the above mentioned and other proper- 

 ties of this substance J 



*Pogg. Ann., cxlix, 577, 1873. f This Journal, Oct. 1880. 



\ In his paper " On the Production and Reproduction of Sound by Light," this 

 Journal, Oct. 188<>, Mr. Bell gives, among other interesting experiments, those on 

 vulcanite. A revolving disc, perforated with holes, produced rapidly recurring 

 flashes of solar rays which impinged on selenium through which passed an electric 

 current. In this circuit were two receiving telephones. The flashes of light caused 

 synchronous alterations in the resistance of the selenium and in the electric cur- 

 rent traversing it ; so that when two leceiving telephones, in the circuit, were 

 placed to the ears a sound was perceived: the frequency of whose vibration corre- 

 sponded to the frequency of the flashes of light. Mr. Bell writes: " We have made 

 experiments with the object of ascertaining the nature of the rays that affect 

 selenium. For this purpose we have placed in the path of an intermittent beam 

 various absorbing substances. When a solution of alum, or bisulphide of carbon, 

 is employed, the loudness of the sound produced is very slightly diminished, but 

 a solution of iodine in bisulphide of carbon cuts off most, but not all, of the 

 audible effect. Even an apparently opaque sheet of hard rubber does not entirely 

 do this. This observation which was first made in Washington, D. C, by Mr. 



