Intelligence and Miscellaneous Articles. 77 



The gases I have examined are hydrogen, atmospheric air, and 

 nitrogen, previously dried by passing over caustic potash or concen- 

 trated sulphuric acid. The red line (a) of hydrogen assumes great 

 splendour as the pressure increases ; and when the tension of the 

 gas is near 40 atmospheres, the red region of the spectrum is so 

 luminous that the line o hardly stands out upon the brilliant back- 

 ground. At this moment the line y is completely dissolved in the 

 most refrangible portion of the spectrum. The lines of the other 

 gases which 1 have examined produce the same effects ; and the 

 least sharp among them disappeared when the pressure became such 

 tliat the luminous current ceased. In these experiments it often 

 happens that the glass is attacked ; then the sodium-line appears 

 very brilliant. When the points of the wires are dipped in a salt 

 of sodium, lithium, thallium, or one of the metals easy to recognize, 

 the lines characteristic of these metals assume a splendour which 

 goes on increasing with the pressure ; and when the gaseous lines 

 are almost effaced, the metallic lines, although much less sharp, are 

 still conspicuous on the spectrum, which has become sensibly con- 

 tinuous. Several experiments have left me the impression that, if 

 it were possible to observe under stronger pressures, continuous 

 metallic spectra would probably be obtained. I have measured the 

 proportion in which the luminous intensity of the spark increases 

 under pressure. For this purpose I employ two induction-coils of 

 the same dimensions, giving sparks of the same intensity. I then 

 compress the gas contained in one of the luminous tubes ; and I can 

 compare, by one of the known means of photometry, the primitive 

 spark with that increased by pressure. I have thus been enabled to 

 prove that, by varying from 1 to 40 atmospheres the tension of the 

 gas in which the spark is produced, the latter becomes at least 200 

 times as bright. In fact a spark which at the atmospheric pressure 

 is scarcely visible, will under pressure light up a spacious laboratory. 



From the facts here stated we may, I think, conclude : — 



(1) That the spark which readily traverses the rarefied gas in a 

 Geissler's tube or the electric Q^g, encounters considerable resistance 

 when produced in compressed gas ; it is likewise probable that the 

 heating of the sides of the tube facilitates the flow of the electricity, 

 as is shown by M. Ilegnaull's experiments. 



(2) That the brightness of the spark obtained under the ordinary 

 pressure becomes at least 200 times as great when the tension of 

 the gas is increased to the point at which the luminous current ceases. 

 This confirms the beautiful experiments of Frankland on the com- 

 bustion of hydrogen under pressure. 



(3) That the luminous intensity of the gaseous lines increases 

 with the pressure, and that at about 40 atmospheres, when the tem- 

 perature must be very high in the vicinity of the wires, those lines 

 almost entirely disappear in the field of the spectrum, which has 

 become very luminous and sensibly continuous. — Comptes Renclus Je 

 VAcad. des Sciences, May 13, 1872. 



FURTHER RESEARCHES ON THE REFLECTION OF HEAT. 

 BY M. P. DESAINS. 



In the sitting of the 22nd of April I had the honour of calling the 



