yune 9, 1881] 



NATURE 



127 



which was with difficulty excluded from the interior of houses. 

 Their duration varied from a few hours to two days ; and from 

 the fact that one of the dust-winds was simultai.eously ex- 

 perienced at Hanliow, Kiukiang, and Chinkiang — a portion of 

 the river's course nearly equal to 450 miles— I may conclude 

 that they were not local phenomena, but pos^essed a consider- 

 able horizontal extension. The dust, which in all respectj 

 resembles the loam forming the banks and alluvial plains of the 

 Yang-tse, is ccmposed of mineral particles and vegetable debris 

 — the former varying from ^J^ to tAts of ^" \r\i^ in tize, and 

 being generally siliceous or calcareous in composition. 



Three dust-winds came under my observation on March 25, 

 April 21, and May I ; all of them possessed the following 

 meteorological conditions: — During the two or three preceding 

 days the barometer fell, whilst the mean daily temperature rose, 

 and in two instances the winds were light and southerly. 

 During the continuance of the dust-winds the barometer ro-e, 

 the mean daily tempeiature ceased to rise, and light winds with 

 a force of 1 and 2 prevailed varying in direction from north to 

 north-east. For a period of a day or two after the dust-winds 

 had ceased the thermometer registered a lower n.ean daily tem- 

 perature, the tiaromeler ccntinued to rise, and the wind retrained 

 the same northerly direction. In all three cases there was a 

 disturled electrical condition of the atmosphere: in the first 

 instance a severe thunderstorm accomj anied by heavy rain 

 occurred on the day following ; the second dust wind was 

 accompanied at its commencement by a little thunder and 

 lightning, but by no rain; whilst during the two days pre- 

 ceding the third dust-wind there was a considerable amount of 

 thunder and lightning, together with heavy rain. 



From this comparison of the prevailing atmospheric condi- 

 tions in connection w ith these dust-winds, a more probable 

 explanation of their occurrence may be obtained, than that 

 which is often proposed when simply assigning a "sudden 

 breeze" and a "hot day" as the conditions required to give 

 rise to them. H. B. Guppy 



: 7, Wood Lane, Falmouth, June i 



A Singular Cause of Shipwreck 



The strange loss of the T/iani.x off the Iceland coast may 

 perhaps lend some interest to the following : — 



Last summer was the best the Icelanders had had for long 

 past. I regret that I can give no ihermometric readings, as my 

 instrument became useless during the voyage. Tf e weather in 

 the north was nearly as warm as it has betn here lately. All the 

 snow-fed rivers were very full. The Jokul-a was nearly up to 

 its high water mark quite early in the seascn, and the Blanda 

 was almost impassable. Icelanders who rede with me said ihat 

 they had never seen the mountains from Hoff's Jokul to Eyrik's 

 Jokul so free from snow. 



I append extracts from a letter which I have just received 

 from one of my guides. A. J. Hubbard 



St. Thou as's Hospital, S.E. , June 4 



( Verbatim copy) 



" Hjedinstrofda, April 16, 18S1 

 "... This winter has been so uncommonly strong that none 

 such has existed this century. The frcst has been extremely 

 severe — 32° R., once at Akurtyii, and 36° \<. (=49j'Fahr.) 

 somewhere with M}vatn. . . . Ptarmigaiis and other tirds froze 

 to death. The farmers had spent most of their hay, and their 

 cattle were to be killed or starve to death. All the sea wcs 

 covered with ice, mostly polar ice, as far as or.e could see from 

 the tops of the mountains. On the 2nd inst. the weather was 

 mild, and on the 7th we had a real thaw, and every day since 



very mild and fine w eather. But it is possible that the ice 



w ill not drive aw ay before late in August, and no ship can come 

 to any harbour on the northern coast ; this happened (also in) 

 1869. " KristjAn J6NASARSON " 



An Optical Illusion 



The optical illusion described in Nature, vol. xxiv. p. 54, 

 is, as I have already mentioned, referred to by Priestley 

 (History, &c.. Vision, Light, and Colours, vol. ii. p. 725). The 

 description is as follow s : — " M. Le Cat well explains a remark, 

 able deception by which a person shall imagine an object to be 

 on the opposite side of a board when it is not so, and also inverted 

 and magnified. It is illustrated by Fig. 162, in which D repre- 



sents the eye ard c B a large black board pierced with a small 

 hole. E is a large white board placed beyond if, and- strongly 

 illun inated, andi/a pin or other small object held betwixt the 

 eye and the first board. In these circumstances the pin shall be 

 imagined to be at F on the other side of the board, where it will 

 appear inverted and magnified, beciuse what is in fact perceived 

 is the shadow of the pin upon the retina ; and the light that is 

 stopped by the upper part of the pin, coming from the lower part 

 of the enlightened board, and that which is stopped by the lower 

 part coming from the upper part of the board, the shadow must 

 necessarily be inverted with respect to the object." ("Traite des 

 Sens," par M. Le Cat, Amsterdam, 1744, p. 298.) 



C. J. Woodward 

 Birmingham and Midland Institute, Birmingham, June 6 



THE VISITATION OF THE ROYAL 

 OBSERVATORY 



'X'HE Report of the Astronomer- Royal to the Board of 

 -'• Visitors on Saturday last at the annual visitation 

 was I'stened to with special interest, and indeed the 

 attendance of astronomers and others at the C bser- 

 vatory was very much larger than usual, because it 

 was generally understood that this would be the last 

 occasion of the kind on which the veteran astronomer 

 would be seen at his post. We learn that an appro- 

 priate address was made to him by the Board of Visitors 

 when he announced his attention of relinquishing his 

 official duties in order to enable him to devote all his 

 time and energies to the researches he has now on hand. 



The astronomical observations, which occupy the first 

 part of the Report, have been carried on with the usual 

 diligence. Most of the routine work of the Observatory 

 seems to have gone on in the usual fashion through the 

 last year. 



One of the objects of interest on this occasion was 

 Halley's ancient tombstone, which, after its removal from 

 Lee Churchyard (where it had been replaced by a new 

 stone with a facsimile of the inscription), had been placed 

 in the South Ground, where it had teen lying for several 

 years. It has now been carefully restored, and mounted 

 on the east wall of the lobby of the North Dome. 



The sun's chromosphere has been e.xamined with the 

 half-prism spectroscope on 29 da)s during the period to 

 which this report refers. Fourteen sun-spots have been 

 examined on 20 days, with reference to the broaden- 

 ing of the lines in their spectra. The results confirm the 

 reivark that some of the lines of iron are broadened in 

 some spots, whilst others arc broadened in other spots. 

 Displacements of some of the lines of iron towards the 

 red, and of others towards the blue, have also been noted 

 in the case of one spot. A remarkable spectrum of a 

 sun-spot showing 17 strong black lines or bands, each 

 as broad as b-^, in the solar spectrum, w-as observed on 

 November 27 and 29, iSSo. These bands, to which 

 there is nothing corresponding in the solar spectrum 

 (except some very faint lines), have also been subse- 

 quently remarked in the spectra of several spots. 



For the determination of motions of stars in the lire of 

 sight, 168 measures have been made of the displacement 

 of the F line in the spectra of 43 stars, 87 of the b^ line 

 in 27 stars, and 8 of the b^ line in 4 of these stars. Of 

 these 70 stars 16 had not previously been examined, and 

 the total number of stars of w hich the motions have been 

 spectroscopically determined is now 91. In the case of 

 6 of the stars observed in the last year, a dispersive power 

 equivalent to that given by 16 prisms of 60" has been 

 used. Ten measures have been made of the relative 

 displacement of the F and b lines in the spectra of the 

 east and west limbs of Jupiter. 



Comet 1810 d (Hartwig's), and the aurora of 1881, 

 January 31, have been spectroscopically e.xamined. 



Between 18S0, May 9, and 1S81, May 13, photographs 

 of the sun were taken on 140 days, and of these 284 have 

 been selected for preservation. There are only 8 days 



