December 20. 1900] 



NATURE 



189 



intended for use in the reduction of meridian measures of the 

 planet. The positions for 77 of these are given at intervals of 

 10 days, and for the remaining four polar stars daily positions. 



Two other observatories have undertaken the special task of 

 determining the co-ordinates of stars for reference — Charkow, 

 directed by M. L. Struve, and d'Abbadia, directed by M. I'Abbe 

 VerschaflFel. 



Many notices have come to hand indicating that a considerable 

 number of successful determinations have been made, and a 

 scheme is being considered to ensure the publication of all the 

 combined results in such form as to be of the greatest service to 

 the observers, and thus any one may be able to have access to the 

 complete data. 



M. de Campos Rodrigues, director of the Lisbon Observatory, 

 writes saying that 743 observations have been made ; helio- 

 metric measures have been commenced at Bamberg, by M. 

 Hart wig ; at the Observatory at Algiers 63 photographs have 

 been taken. 



Both at Paris and Algiers it has been found that an exposure 

 of six minutes is sufficient to record stars as faint as 12-5 magni- 

 tude, and from special trials it is considered that with this ex- 

 posure it is certain that a sufficient number of compaiison stars 

 will be obtained surrounding the planet. Prof. Hale has for- 

 warded the times of observation at which Prof. Barnard has 

 taken micrometer measures with the 40-inch Yerkes telescope, 

 and a comparison shows that several of these, made during the 

 first part of the night, correspond almost directly with others 

 obtained at European observatories (Paris and Cambridge) 

 uuiing the second part of the night. 



A letter from Prof Comstock is also included, giving par- 

 ticulars for the accurate determination of the diurnal motion. 



Marking on Mars. —A Circular received from the Central- 

 s'elle at Kiel announces a message from Prof. Pickering, who 

 on December 8 received a telegram from Mr. Douglass, of the 

 Lowell Observatory, Flagstaff, Arizona, stating that he had 

 observed a projection on the northern edge of the Icarium 

 Mare which remained visible for seventy minutes. 



SPECTROSCOPIC INVESTIGATIONS OF 

 GASE^ IN A TMO SPHERIC AIR} 



1 N August last some tubes were filled at low pressure by an 

 improved process wiih the more volatile gases of the atmo- 

 sphere.^ The air was liquefied directly from that above the roof 

 of the Royal Institution by contact at atmospheric pressure with 

 the walls of a vessel cooled below - 200° C. When about 

 200 c.c. of liquid had condensed, communication with the outer 

 air was closed by a stop-cock. Subsequently communication 

 was opened, through another stop-cock, with a second vessel 

 cooled by immersion in liquid hydrogen, and a part of the liquid 

 from the first vessel, maintained at -210°, was allowed to distil 

 into the second still colder vessel. When about loc.c. had con- 

 densed in the solid form in the second vessel, communication 

 with the first vessel was cut off, and a manometer showed a 

 pressure of gas of about 10 to 15 mm. of mercury. 



This mixture of gases was passed into tubes previously 

 exhausted by a mercury pump, but before reaching the tubes it 

 had to pass through a U-tube immersed in liquid hydrogen so as 

 to condense less volatile gases, such as argon, nitrogen, oxygen 

 or carbonic oxide, which might be carried along by those more 

 volatile. Previous trials with tubes filled in the same way, 

 except that the U-tube in liquid hydrogen was omitted, showed 

 that these tubes contained traces of nitrogen, argon and com- 

 pounds of carbon. The lubes filled with gas which had passed 

 through the U tube showed on sparking no spectrum of any of 

 these last-mentioned gases, but showed the spectra of hydrogen, 

 helium and neon brilliantly, as well as a great many less brilliant 

 rays of unknown origin. In addition, they showed at first the 

 brightest rays of mercury, derived no doubt from the mercury 

 pump by which they had been exhausted before the admission of 

 the gases from the liquefied air. After some sparking the mercury 



1 " On the Speclrum of the more Volatile Gases of Atmospheric Air, which 

 are not Condensed at the Temperature of Liquid Hydrogen." Preliminary 

 notice by Prof. G. D. Livemg and Prof. Dewar. — Read before the Royal 

 Society on December 13. 



2 In this paper we describe researches in continuation of those previously 

 communicated to the Socittv by one of us, in a paper entitled " Application 

 of Liquid Hydrogen to the I'nduction of High Vacua, together with their 

 spectroscopic Examination," Roy. Soc. Proc. vol. 64, p. 231. 



NO. 1625, VOL. 63] 



rays disappeared, probably in consequence of absorption of the 

 mercury by the electrodes, which were of aluminium. 



In one experiment the mixture of gases in the second vessel, 

 into which a fraction of the liquefied air was distilled as above 

 described, was pumped out without being passed through the 

 U-tube in liquid hydrogen and examined. This mixture was 

 found to contain 43 per cent, of hydrogen, 6 per cent, of oxygen, 

 and 51 per cent, of other gases — nitrogen, argon, neon, helium, 

 &c. — and it was explosive when mixed with more oxygen. 

 This shows conclusively that hydrogen in sensible proportion 

 exists in the earth's atmosphere, and if the earth cannot retain 

 hydrogen or originate it then there must be a continued acces- 

 sion of hydrogen to the atmosphere (from interplanetary space), 

 and we can hardly resist the conclusion that a similar transfer of 

 other gases also must take place. The tubes containing the 

 residue of atmospheric gases uncondensed at the temperature of 

 liquid hydrogen we have examined spectroscopically. 



On passing electric discharges through them, without any 

 condenser in the circuit, they glow with a bright orange light, 

 not only in the capillary part, but also at the poles, and at the 

 negative pole in particular. The spectroscope shows that this 

 light consists in the visible part of the spectrum chiefly of a 

 succession of strong rays in the red, orange, and yellow, attri- 

 buted to hydrogen, helium and neon. Besides these, a vast 

 number of rays, generally less brilliant, are distributed through 

 the whole length of the visible spsctrum. They are obscured in 

 the spectrum of the capillary part of the tube by the greater 

 strength of the second spectrum of hydrogen, but are easily seen 

 in the spectrum of the negative pole, which does not include 

 the second spectrum of hydrogen, or only faint traces of it. 

 Putting a Leyden jar in the circuit, while it more or less com- 

 pletely obliterates the second spectrum of hydrogen, also has a 

 similar effect on the greater part of these other rays of, as yet, 

 unknown origin. The violet and ultra-violet part of the 

 spectrum seems to rival in strength that of the red and yellow 

 rays, if we may judge of it by the intensity of its impressions on 

 photographic plates. We were surprised to find how vivid 

 those impressions are up to a wave length 314, notwithstanding 

 the opacity of glass for rays in that part of the spectrum. The 

 photographs were taken with a quartz calcite train, but the rays 

 had to pass through the glass of the tube containing the gases. 



We have made approximate measurements of the wave- 

 lengths of all the rays which are sufficiently strong to be seen 

 easily or photographed with an exposure of thirty minutes, and 

 give a list of them below. These wave-lengths are computed to 

 Rowland's scale, and were deduced from the deviations pro- 

 duced by two prisms of white flint glass for the visible, and of 

 calcite for the invisible, rays. The wave-lengths assigned to the 

 helium lines are those given by Runge and Paschen, and some 

 of these lines were used as lines of reference. In general, the 

 iron spark spectrum was the standard of reference. 



The tubes when first examined showed the lines of the first 

 spectrum of hydrogen vividly, and the earlier photographs of 

 the spectrum of the negative pole contained not only the violet 

 lines of hydrogen, but also the ultra-violet series as far up as 

 A. 337. In order to get impressions of the faintest rays, exposures 

 of half an hour or more were required, and a succession of photo- 

 graphs had to be taken so as to get different sections of the 

 spectrum into the middle of the field, where measurement of the 

 deviations would not he impeded by the double refraction of the 

 calc spar. As the light of the negative pole only was required, 

 the electric discharge was made continuously in one direction 

 only, with the result that the hydrogen lines grew fainter in each 

 successive photograph, and soon disappeared altogether. Along 

 with the ultraviolet rays, the less refrangible rays of hydrogen 

 also disappeared, so that no trace of the C or F line could be 

 seen, nor yet of the second spectrum, so long as the current 

 passed in the same direction as before. Reversal of the current 

 soon made the F line show again, so that it seems that the whole 

 of the hydrogen was driven by the current to the positive pole. 

 The conditions under which this ultra-violet series shows itself 

 are a matter of interest. It appears here in the midst of a 

 brilliant spectrum due to gases other than hydrogen, and yet it 

 is very difficult to obtain a photograph of it when no gas but 

 hydrogen is known to be present, or, at least, to become 

 luminous in the electric discharge. 



We have had an opportunity of comparing the spectrum of 

 the volatile residue of air with that of the more volatile part of 

 gas from the Bath spring. The tube did not admit of the 

 separate examination of the light from the negative pole, but 



