Dec. 20, 1888] 



NATURE 



183 



within him, appalled before the host of difficulties ; as 

 when, for example, the shadow of a passing cloud on a 

 sunny day reveals to him the individuality of the 400 plants 

 in each square foot of pasture, which have before escaped 

 his attention, and the thought flashes across his be- 

 wildered mind of the 400 parts played by each plant, and 

 the 400 times 400 causes that effect them. Almost hope- 

 lessly he perceives that the knowledge which he is in 

 search of, and which he fancied he had in his hand, has 

 eluded his grasp like a fire-fly, and left only a flash 

 behind ; and for a moment his mind is enveloped in 

 darkness, overpowered by the infinity of Nature. The 

 searcher after truth, however, recovers, recognizes his 

 difficulties, recalls the object of his pursuit, returns to it 

 with renewed energy, and, with unbiassed mind, records 

 his observations day by day. 



ALPINE HAZE. 



'~Y HAT no letter has appeared on the common occur- 

 *■ rence of this phenomenon in the British Isles is one 

 of a thousand tokens of the small amount of interest in 

 atmospheric phenomena taken by the public in this 

 country. In bright days when the atmosphere at the 

 earth's surface is nearly calm and moderately dry, the 

 sky being nearly devoid of clouds, horizontal layers of 

 butT-coloured haze may be frequently seen near the horizon 

 in almost every locality in the British Isles where the air 

 is free from the smoke of our large towns. I do not hap- 

 pen to have seen it nor have I heard of its occurrence on 

 the west coasts of Scotland or of Norway. I have fre- 

 quently noticed it when out of sight of land. It would 

 be interesting to know whether it is seen at a distance of 

 400 or 500 miles from the nearest shore. At St. Aubin's, 

 Jersey, at an elevation at which the French coast near 

 St. Malo is rarely visible, a stria of this haze is often the 

 accompaniment of mirage, the inverted image of the 

 white-tipped rocks appearing to hang from the layer of 

 haze, and the mirage disappearing with a change of the 

 observer's elevation, but the line of haze remaining visible 

 The mirage was, when first seen, mistaken for a few 

 minutes by some members of my family for a series of 

 water-spouts. 



I have long ago given the specific name of nebula arida, 

 " dust-haze," to the phenomenon dealt with in this letter; 

 and I still think that the English title " dust-haze" is pre- 

 ferable to " earth-haze," or any equivalent of the former 

 to any of the latter in foreign languages, the latter term 

 being too general, and capable of including the haze or 

 mist produced by the presence of water particles. The 

 word "dust' does not exclude organic matter, although 

 ordinary dust-haze consists in most cases, as I think, of 

 inorganic particles. On the other hand, any name which 

 appears to localize the phenomenon is scarcely admissible. 

 Dust-haze may be somewhat easily distinguished from 

 ordinary mist or water-haze by its colour appearing of 

 a reddish-buff tint in reflected light ; and unless in com- 

 plete shade from direct light, rarely becoming neutral ; 

 whereas mist usually appears gray, neutral, or bluish 

 in reflected light, and yellow, orange, or red in trans- 

 mitted. Patches—or, as they appear at a distance, 

 bands— of dust-haze often become beds of the under 

 surface of cumuli, to the formation of which clouds 

 they then seem to bear a causal relation. As frequently 

 in our islands, the haze is replaced during the night by 

 stratiform clouds at its own level. In these cases there 

 can be, I think, little doubt that the solid particles cause 

 the precipitation of vapour. This fact somewhat militates 

 against M. Antoine d'Abbadie's theory that the haze is 

 really dry air, a supposition which for other reasons I 

 regard as untenable. 



Seen near the sun at sunset, bands of dust-haze are 

 mistaken by many observers for threads of cirrus (what 



I ierm cirro-filum), and moreover the two phenomena are 

 not uncommonly seen at the same time. As observations 

 at sunset are useful in forecasting weather, the observers 

 should take care to remember that lines of cirrus are 

 always more illuminated in transmitted light than any 

 species either of haze or of stratus cloud ; secondly, that 

 the cirrus threads appear slightly arched when viewed 

 across the Hne of sight, and radiating when more coinci- 

 dent with it ; and lastly, that a slight curl here or there 

 ver)' often betrays the existence of the lofty ice-cloud. I 

 have frequently given rough sketches of these latter sun- 

 sets to observers, and these have borne a singular likeness 

 to Antoine d'Abbadie's sketch of the dust-haze itself 

 (Nature, November 22, p. 79). But I do not understand 

 this sketch, or in what sense it represents two horizontal 

 bands. 



In conclusion, I may perhaps be permitted to refer to 

 two phenomena slightly related to the subject of this letter. 

 The first is smoke. This is much more "accumulated" 

 or less amorphous than water-dust, although its optical 

 characteristics resemble somewhat closely those of water- 

 dust. On the other hand, it is much more amorphous 

 than dust-haze ; and even the line left in the atmosphere 

 by a steamer on the sea horizon on a calm day will scarcely 

 be mistaken for dust-haze. Smoke when at a consider- 

 able elevation undoubtedly produces cumuli under favouf- 

 able conditions. A string of ill-defined cumuli may be 

 seen in the smoke of a burning forest or heath when 

 carried a long way from land by a wind from the shore. 

 This condensation is probably principally caused by the 

 presence of solid particles, as in the case of dust-haze, 

 but it may be borne in mind that a large quantity of 

 vapour is carried up with smoke. 



Lastly, the keen eye will soon learn to distinguish a 

 peculiar haze often noticeable in England, especially over 

 the wheat-producing districts, in fair calm weather in the 

 month of Septem.ber. This haze is also visible in some, 

 and probably in many, parts of continental Europe. It 

 is caused by flying Aphides, ten or more of which may 

 be often captured in a cubic yard of air at about 10 feet 

 from the earth's surface. In reflected light the haze has 

 a tint of tender ultra-marine ash. 



W. Clement Ley. 



Lutterworth, December 8. 



NOTES. 



Mr. Ralph Copeland, Ph. Doc, F.R.A.S. ha? been 

 appointed Astronomer Royal for Scotland, and Professor of 

 Practical Astronomy in the University of Edinburgh, in the 

 room of Prof. Piazzi Smyth, resigned. Prof. Copeland his 

 proved himself to be among the most skilful of modern 

 observers. 



M. DiTTE has been elected to succeed the late Prof. Debray 

 at the Sorbonne. 



The Paris Municipal Council will shortly be asked to grant 

 the funds required by Prof. Giard to provide a laboratory and to 

 secure the necessary assistants. 



We refer elsewhere to-day to the dinner given on Tuesday, 

 the nth inst., at Christ's College, Cambridge, to celebrate the 

 completion of the ninth edition of the " Encyclopaedia Briuin- 

 nica." The chair was of course occupied by Dr. Robertson 

 Smith, the editor. Among the scientific contributors present 

 were Sir Frederick Abel. Dr. Affleck, Sir Nathaniel B.irnal y, 

 Dr. Buchan, Prof. Cayley, Prof. Darwin, Mr. F. Darwin, 

 Prof. Diitmar, Prof. Michael Foster, Dr. A. Geikie, of the 

 Geological Survey, Dr. Glaisher, Sir F. Goldsmid, Prof. Cleland, 

 Prof. Marshall Ward, Dr. Creighton, Prof. Greenhill, Dr. 

 Giinlher, Sir Charles Hartley, Baron von Ilujel, Prof. Keane, 



