I04 



NATURE 



{May 30, T88-9 



of direction, the wind became so favourable that we could 

 use sails on the sledges, and thus they became less heavy 

 to pull. In this manner we advanced during three days, 

 then the wind went down, and we were obliged to lower 

 our sails. 



" In the beginning of September we reached a quite flat 

 and extensive plateau, which resembled a frozen ocean. 

 Its height was between 8000 feet and 9000 feet, though 

 towards the north it seemed to be considerably higher. 

 Over this plateau or highland we travelled more than two 

 weeks. The cold was considerable. I am not, however, 

 able to give an exact statement of the temperature, as our 

 thermometers did not go low enough. I believe that on 

 some nights it was between - 45° and - 50° C. (between 

 80^ and 90' F. below freezing point) In the tent where we 

 (six men) slept, and where we cooked our tea and 

 chocolate, it was even less than- 40"^ C. (72^ F. of frost). 

 During one month we found no water. To get drinking- 

 water we were obliged to melt snow either in our cooking 

 apparatus or by our own warmth in iron bottles, which 

 were carried inside our clothes on our bosoms. The sun- 

 shine on these white snow-fields was bad for the eyes, but 

 no case of snow-blindness occurred. Only one day, 

 September 8, we were stopped by a snowstorm ; the next 

 day, when we wanted to continue our journey, we found 

 the tent was quite buried in the snow. 



" On September 19, we got a favourable sailing wind, 

 and then we advanced very rapidly. That day we got the 

 first sight of the mountains of the west coast. In the 

 night we were stopped by dangerous ice with many 

 crevasses, after having very nearly lost several men and 

 sledges in one of them. We met here with very difficult 

 and uneven ice, where we advanced very slowly. At last 

 on September 24, we reached land at a small lake to the 

 south of Kangersunok, a fjord inside Godthaab. On 

 September 26, we reached the sea at the inner end of the 

 Ameralik fjord, in 64'' 12' N. latitude." 



This really finished the journey across Greenland. 

 With considerable difficulty the party reached Godthaab, 

 where, as the last ship was gone, they had to spend the 

 winter, reaching Copenhagen only last week. So far Dr. 

 Nansen has not been able to tell us much more than 

 we knew already about the interior ice of Greenland ; though 

 he will probably give us full details in the paper which he 

 is to read at the Koyal Geographical Society on June 24. 



ON THE TELLURIC ORIGIN OF THE OXYGEN 

 LINES IN THE SOLAR SPECTRUM} 



M EIFFEL having very obligingly put the tower 

 • in the Champ-de-Mars at my disposal for any 

 experiments and observations that I cared to make there, 

 I decided to take advantage of the powerful electric light 

 which had been installed, to make certain studies of the 

 telluric spectrum, and, in particular ,that which relates 

 to the origin of the lines of the spectrum of oxygen in the 

 solar spectrum. 



We know now that there exist in the solar spectrum 

 many groups of lines that are due to the oxygen contained 

 in our atmosphere ; but one may ask himself whether 

 these groups are due exclusively to the action of our 

 atmosphere, and the solar atmosphere between counts for 

 nothing, or whether their origin is double — in a word, Are 

 these groups purely telluric or telluric-solar ? 



To settle this question, one may have recourse to a 

 certain number of methods. One of the most trustworthy 

 is that of displacement, the origin of which rose from the 

 beautiful conception of M. Fizeau, and which has been 

 applied by M. ThoUon and perfected by M. Cornu. 



• Translation of a paper read by M. J. Janssen before the French 

 Academy of Sciences on May 20, 1889 (jOom^tes rendits, cviii. No. 20). 



The application of this was too difficult in the present 

 case. 



We may also observe the diminution of intensity which 

 the groups undergo when we ascend in the atmosphere, 

 and by careful comparisons when possible, and especially 

 by a great number of observations, we may judge if the 

 diminution of the intensity of the lines would permit us 

 to conclude that they would completely disappear at the 

 limits of the atmosphere. This is the method employed 

 in the last Mont Blanc expedition (Grands-Mulets). Or, 

 we may again proceed with a comparison of the uniformity 

 of the lines by installing a powerful light giving a con- 

 tinuous spectrum at such a distance that the thickness of 

 atmospheric air traversed may have the same action as 

 that of the terrestrial atmosphere on the rays of the sun, 

 when it is near the zenith. 



This last circumstance is very fortunately found realized 

 in the respective situations of the Eiffel Tower and the 

 Meudon Observatory. The tower is at a distance from 

 the Observatory of about 7700 metres, which very nearly 

 represents the thickness of an atmosphere having the 

 same weight as the terrestrial atmosphere and a uniform 

 density, and equal to that of the atmospheric layer 

 traversed by the sun's rays. 



In addition to this, the considerable power of the 

 magnificent light actually installed on the summit of the 

 tower permits the employment of the instrument that had 

 served me at Meudon and at Grands-Mulets for the sun. 

 I have, however, made use of a condensing lens in front 

 of the slit in order to give the spectrum an intensity quite 

 comparable to that of the solar spectrum in the same 

 instrument. 



Under these conditions the spectrum is shown with, 

 extreme vividness, and extends beyond A. The B group 

 appeared to me as intense as with the sun on the 

 meridian in summer. The A group was equally 

 well defined. Other groups could be distinguished,, 

 and notably those of water-vapour, their intensity show- 

 ing the hygrometric state of the column of atmosphere 

 traversed. 



I should have liked to study the oxygen groups with the 

 great spectrometer of MM. Brunner and a Rowland's grat- 

 ing, but the limited time during which the light was turned 

 on to me did not permit it. I hope to do so another 

 time. 



Not one oxygen band is seen in the visible spectrum, 

 although the thickness of the layer of oxygen traversed 

 was equivalent to a column of more than 260 metres of 

 oxygen at a pressure of six atmospheres — that is to say, 

 at the pressure under which the tube in our laboratory 

 shows them with a length of only 60 metres, or four times 

 as small. This well shows that, for oxygen, the lines follow 

 an entirely different law from the bands. 



Indeed, whilst for the lines the experiment of last 

 Sunday shows us that it appears indifferent whether we 

 employ a column of gas at constant density or a column 

 equivalent in weight but with variable density ; for the 

 bands, on the contrary, the absorption taking place follow- 

 ing the square of the density, the calculation shows that 

 there would be required, at the surface of the sun, a 

 thickness of atmosphere of more than 50 kilometres to 

 produce them. 



I do not look upon the experiment of last Sunday as 

 more than bringing forward a fact more to a group of 

 studies— a fact which requites to be exact and developed. 

 But it is certain to myself, that the height at which the 

 tower of the Champ-de-Mars makes it possible to place 

 the light source, and its power, v/ill enable me to make 

 other similar experiments of higher interest. 



Before concluding, I wish to thank M. Eiffel for the 

 liberality with which he put his beautiful edifice at the 

 disposal' of science. I equally thank MM. Sautter and 

 Lemonnier for their kir.dr.ess. 



