542 Scientific Intelligence. 



obtained from experimental data, by Eucken, for the specific 

 heat of hydrogen at very low temperatures. It is shown that 

 "Eucken's results for the specific heat of hydrogen make the 



existence of an amount of energy — — » at the absolute zero, prob- 

 able." Furthermore, the authors show that " The hypothesis of 

 energy at the absolute zero opens a way for deriving Planck's 

 radiation formula without the introduction of any kind of discon- 

 tinuity whatsoever." "It appears doubtful, however, whether 

 the remaining difficulties can be overcome without the assumption 

 of quanta." — Ann. d. Phys., No. 3, March 1913, p. 551. 



h. s. u. 



7. The Electric Carbon Arc at Low Pressures. — The recent 

 investigation of the carbon arc at pressures less than one atmos- 

 phere by M. La Rosa has brought to light some interesting facts. 

 The lamp consisted essentially of two inclined carbon rods enclosed 

 in a large glass bell-jar. The distance between the poles was 

 controlled by an automatic regulator. When the air pressure in 

 the jar was decreased to a few centimeters of mercury the arc 

 showed no remarkable changes either electrically or optically. 

 The current remained practically constant, the voltage across the 

 arc decreased slightly, and the length of the arc increased, thus 

 showing that the current passed more readily as the pressure was 

 lowered. The spectrum showed a decrease in the intensity of the 

 second group of cyanogen bands, On the other hand, when the 

 pressure was reduced to a few millimeters the arc gradually 

 changed its essential form and appearance. The core, formed by 

 the anode and cathode flames, and the mantle no longer pos- 

 sessed sharply defined boundaries. The mantle became almost 

 invisible while the core altered to a diffuse luminous region in 

 which various bright and dark parts could be seen. On the whole, 

 the arc at low pressures possessed the well-known characteristics 

 of the discharges in vacuum-tubes. Although the arc changes 

 gradually from the one "regime" to the other as the gas pressure 

 is varied, the investigator convinced himself of the existence, of 

 two distinct regimes by the following test: At 5 mms pressure and 

 with a resistance of about 19 ohms in the line the current was 5*1 

 amperes, the drop across the arc was 53 volts, and the length of 

 the arc was I4 mms . When the series resistance was increased to 

 about 22 ohms the arc changed abruptly to the usual type, while 

 the current, the voltage drop, and the arc length assumed the 

 values 5*3 amperes, 34 volts, and 2 mms respectively. This process 

 was completely reversible. 



The spectrum of the arc at low gas pressures (2d regime) dif- 

 fered from that at higher pressures (1st regime) in two general 

 respects: (a) in the distribution of intensities of the various com- 

 ponent parts of the spectrum, and (b) in the presence of ele- 

 ments which do not occur in the ordinary arc. Thus, although 

 the carbon bands seem to remain unchanged, the cyanogen bands 

 nearly disappear. Moreover, the bands of this compound are not 



