Intelligence and Miscellaneous Articles. 155 



lampblack raised to the same temperature sends out a thermal ra- 

 diation whose intensity is „ MhrA . =57*73, compared with that of 

 the flame. °" 01744 



6. The electric light includes, as is known, two sorts of radiations 

 — viz. the rays emitted by the incandescent carbons, and those 

 emitted by the voltaic arc which springs between the polar extremi- 

 ties of the carbons. The former give a white, the others a purple- 

 blue light ; the resulting light is bluish white. 



7. The two polar extremities have temperatures very different 

 the one from the other. The number of degrees which expresses 

 their temperature can be deduced from the formula 



y-mT\T-d)-n(T-d\ 



supposing that the carbons have the maximum emissive power. 



8. The voltaic arc has very little thermal emissive power, com- 

 parable to that of the pale blue flames of Bunsen burners. Its tem- 

 perature can also be obtained with the aid of the preceding formula, 

 provided that the value of the thermal emissive power of the voltaic 

 arc relative to its thickness be introduced. 



9. A great number of experiments have given the maximum tem- 

 perature of about 3900° C. for the positive, the temperature of 

 about 3150° for the negative polar extremity of the carbon. For 

 the voltaic arc which springs between these two extremities the 

 temperature was always about 4800°, whatever the thickness of the 

 arc and the intensity of the current. — Comptes JRendus de V Academic 

 des Sciences, Nov. 10, 1879, t. lxxxix. pp. 781-783. 



ON SOME NEW LUMINOUS TUBES. BY M. TKEVE. 



If the induced current of a Ruhmkorff coil is passed into a 

 Fizeau's condenser, the vibratory motion of the coil is returned, 

 amplified, by the condenser in the form of a well-known kind of 

 humming sound. If pressure, at first slight, and then gradually 

 increasing, be exerted upon the condenser, the humming succes- 

 sively diminishes in intensity and at last dies away altogether. 



The cessation of the sound will be coincident with a pressure 

 capable of expelling from the condenser the air which was interposed 

 in the intervals between its tinfoil sheets. The condenser is then 

 as in a vacuum ; and no sound can issue from it. This observation 

 led me to make the following experiment. 



Into a large G-eissler tube I introduce a Fizeau's condenser. The 

 two poles of the induced current of the Euhmkorff end at the con- 

 denser through the intermediation of the ordinary electrodes of this 

 kind of tubes, which, fused into the glass, are fixed to the eleventh 

 and twelfth sheets of tinfoil*. 



When the induced current passes into the condenser, the tube 

 still containing air at the atmospheric pressure, the usual humming 

 is heard. If vacuum be gradually produced in the tube, the hum- 



* I experimented on a condenser of twelve sheets, carefully prepared 

 by MM. Alvergniat. 



