NA TURE 



\_Nov. I, 1 88: 



be limited to a simple communication of the more 

 interesting results obtained by us from August 17 to 

 September 22. 



On reaching the summit of the Pic du Midi (2877 

 metres), where the barometer maintains a mean height 

 of 538 mm., everything presents itself to the observer as if 

 the density of the veil formed above him by the atmosphere 

 were diminished by about a third. The aerial region left 

 behind him being unquestionably the most charged with 

 mist, dust, and aqueous vapour, he may expect to find at 

 once more light and less diffusion. Thus, during the 

 mornings of September 19 and 20, by masking the sun 

 with a screen held at some distance, and exploring the 

 surrounding space with a small spectroscope with an 

 aperture of o'02ra., we were able to observe the planet 

 Venus at a distance of z' from the solar disk. We could 

 c\en subsequently distinguish it with the naked eye. But 

 what most surprised us was the marvellous definition at 

 this station. The limb of the sun projected on the slit 

 of a spectroscope showed a spectrum with a boundary as 

 sharp as if produced by a punching machine. We can 

 positively state that we never elsewhere saw anything 

 similar either at Nice, in Italy, Algeria, or even Upper 

 Egypt. We should add that this complete absence of 

 undulation was noticed only in the morning. After 

 the slopes of the mountains had been exposed for several 

 hours to the heat of the sun, the undulations were produced 

 as they are everywhere else, and even became excessive 

 for the rest of the day. 



During clear nights, using a telescope with an aperture 

 of o'l6m., and a reflector by Henry of o'2om., we found 

 the perfect definition observed in the case of tlie sun in 

 the morning reproduced in the case of the moon, planets, 

 and stars. Under such conditions observations of extreme 

 precision could certainly have been obtained. 



For the study of solar physics we had set up the 

 horizontal telescope and the large spectroscope which we 

 usually employ. On observing the solar spectrum at 

 a favourable moment, it seemed streaked in its entire 

 length with a considerable number of fine lines, some 

 bright, others dark, at a mean distance of 3" of arc 

 from each other. They certainly belonged to the solar 

 image, for they followed all its displacements, and they 

 could have arisen from the granulations of the photo- 

 sphere alone. Under the same conditions, that is, when 

 the images were perfectly still, the hydrogen bands C and 

 F had no longer any sort of continuity, but seemed 

 formed of distinct bright and dark fragment?, of the 

 same magnitudes as the intervals between the lines.^ This 

 phenomenon was observed not merely at certain times and 

 places, but constantly over the whole surface of the disk. 

 We feel satisfied that the chromosphere presents a 

 system of granulations analogous to that of the photo- 

 sphere. The two systems thus superimposed become 

 separated in the spectroscope, yielding, one a continuous, 

 the other a linear, spectrum, and blending together in the 

 telescope as on a photographic proof If this chromo- 

 sphere, thus rendered visible on the full disk, happened 

 to be traversed by a protuberance, the band C increased 

 in luminosity and for a greater length. By giring suffi- 

 cient breadth to the aperture, we were then able to observe 

 the protuberance itself, as when on the edge, although 

 naturally with less brilliance, and foreshortened. Nor is 

 this the first instance of protuberances thus observed on 

 the full disk. On this subject the delicate observations 

 of Young and Tacchini are well known. But instead of 

 being accidentally visible, instead of being produced only 

 under special circumstances, as for instance in the neigh- 

 bourhood of a spot or on the bridge of a spot in process 

 of segmentation, these phenomena were constant for us 

 with varying degrees of intensity, and under the sole con- 

 dition of using an image entirely free from undulations. 



' These phenomena referretl tj by Messrs. Thollon and Tripled were 

 bservcd and recorded in England under exceptionally fine atmospheric con- 

 tions during the last suns 



The observations made outside the edge of the solar 

 disk were no less pregnant with results. We know that 

 in the spectrum of the chromosphere there are eight lines 

 always visible under ordinary conditions. On the Pic du 

 Midi, during the five days when we were able to make 

 our records at favourable moments, we saw the number 

 of these bright lines always visible increased to over 

 thirty in the portion of the spectrum which is comprised 

 between U and F. Here we subjoin a table of the wave- 

 lengths of these lines : — 



5122-6 



5114-4 



5II2-I 



50S7-0 

 5029 -s 

 50I7-9 

 4983-6 



4923'° 

 4SS2'9 

 4854-2 



It will be seen that, at the altitude at which our obser- 

 vations were made, an approach was made to the condi- 

 tions prevailing during a total eclipse. 



To resume. The observations we were able to make 

 on the Pic du Midi during the five weeks of our sojourn 

 on its summit justify us in concluding that science will 

 gain much by the completion of the astronomical station 

 begun by the directors of the Paris and Pic Observato- 

 ries. Here we should have a permanent establishment 

 always open to savants wishing to undertake special 

 researches. To mention those points only towards which 

 our attention was mainly directed, we are of opinion that 

 good opportunities would here be found of furthering the 

 solution of many problems connected with solar physics 

 and the spectral analysis of the stars. 



THE WHEAT HARVEST O/^ 1883 



THE public must be somewhat puzzled with the 

 divergent opinions of authorities upon the yield of 

 the wheat crop of the present year. On the one side, for 

 example, stands Sir John Lawes with his accurate 

 balances and wonderful wheat field, which experience has 

 taught him usually proves a fair criterion of the yield of 

 the English crop. On the other side is arrayed a some- 

 what formidable party, which we may take as well repre- 

 sented and led by the very able article in the Times of 

 Saturday last, headed " The Result of the Harvest." To 

 put the matter briefly, there is a difference of opinion as 

 to whether we have reaped an average crop or an under- 

 average crop of wheat. And there is also a good deal of 

 difference in opinion as to what an average crop is. The 

 point of greater interest no doubt to us is whether we have 

 just secured an abundant harvest or not. It is a point of very 

 great importance not only intrinsically but as a matter of 

 opinion. If business men believe that our national wealth 

 has been recently increased by an unusual augmentation 

 of our food supply, they may make this opinion a basis 

 for enterprise or speculation. If the opinion which 

 prompted them to action should prove a false one, the 

 results would be inflation, panic, and loss. It is therefore 

 very essential that public opinion should be guided in a 

 right direction upon this important point. .Any person 

 who has read our leading newspapers carefully upon the 

 subject of harvests for a series of years will probably 

 have observed a tendency to over-estimate production. 

 The prospect is usually depicted coulcii)- dc rose, and the 

 public is congratulated upon its harvest prospects, w-hile 

 practical farmers remain in doubt as to the yield of their 

 cornfields. Of one thing we may be certain — that wheat 

 needs heat. The average temperature of our islands is 

 scarcely suitable to the wheat plant, which is rightly viewed 

 as somewhat exotic in its requirements. A slight elevation 

 above the sea-level, or a slight decrease in solar heat,invari- 



