154 



HARDWICKE'S SCIENCE-GOSSIP. 



My last excursion was to Tunbridge Wells, late 

 in August. Of course this being on the Weald 

 is not an orchid locality. I noted a vast abundance 

 of Orchis mascida, many still in flower, but mostly 

 seeded. 



Regarding orchids and the mild weather which we 

 experienced at Christmas, I must state that on Christ- 

 mas Day I noted Aceras atithropophora. Orchis vias- 

 ciila, O. maciilata, Gynuiadenia conopsca and Listera 

 ovata, showing their foliage in a situation facing the 

 north-east where they had been planted last summer. 

 Allium ursitium was also coming up. 



I am only a young beginner in botany, but may 

 my success incite others to take up the study of 

 plants. Nothing, I can assure them, is more health- 

 giving and pleasurable than the glorious rambles 

 which this branch of science necessitates. 



Cambenvell. H. F, Turner. 



RECENT RESEARCHES ON THE METEORIC 

 DUST OF THE SCIROCCO. 



FROM time to time fine dust, having nearly the 

 same composition as certain meteorites, has 

 fallen upon various parts of the earth's surface. 

 Arago writes — " L' observation attentive des chutes 

 des poussieres fait presumer qu'elles ne different pas 

 essentiellement des chutes d'aerolithes ordinaires." 

 Prof. Silvestri, of Catania, recently collected some 

 dust which fell in Sicily, and found it to contain not 

 only metallic iron, but also nickel and various silicates 

 and phosphates such as are commonly found in 

 meteoric stones. He is, therefore, inclined to 

 believe either that the dust has been abraded from 

 meteorites, or that it circulates in space, and is 

 attracted to the earth's surface when it penetrates 

 within the atmosphere. 



Professor Tacchini, who has exchanged the obser- 

 vatory of Palermo for that of the Collegio Romano, in 

 Rome, has recently published a lengthy memoir 

 entitled ^^ Sulk polveri meteoriche di Scirocco raccolte 

 i)i Italia e segnatamcntc in SiciliaP He was assisted 

 in his researches by Professor Macagno and Ricco, and 

 a resume of the results at which they arrived was 

 recently read before the meteorological section of the 

 French Association for the Advancement of Science 

 at Algiers. The memoir contains some beautifully- 

 executed microscopic drawings of the appearance of 

 the meteoric dust when highly magnified, and by a 

 series of small maps showing the barometric curves 

 for the periods during which the dust fell. 



The chemical examination of the dust which fell 

 in 1879 in various parts of Sicily and Italy gave the 

 following result. Water, alcohol, and ether had 

 a scarcely sensible action upon it ; but from some 

 specimens alcohol dissolved out a greenish colouring 

 matter — the chlorophyll contained by the vegetable 

 matter of the dust. The ordinary mineral acids 



produced a considerable eff'ervescence, due to the 

 escape of carbonic anhydride. A certain quantity 

 of the substance remained undissolved by aqua regia. 

 The complete analysis of a greyish-red dust which 

 fell at Palermo on May 17th, 1879, was made by 

 Professor Macagno. 



Hygroscopic water 2*221 



Organic matter ....... 19*762 



Carbonic acid ...... 10*672 



Sulphuric acid ...... 3*670 



Phosphoric acid ...... 0*903 



Potassium oxide ...... 1*481 



Sodium oxide ...... 0*915 



Calcium oxide ...... S'542 



Magnesium oxide ...... a'oiS 



Aluminium oxide ...... 0*157 



Metallic iron ....... o'296 



Sesquioxide of iron and metallic iron . . 1*215 



Oxide of nickel ...... 0*046 



Oxide of cobalt ...... 0*005 



Silica 49*982 



Loss •...•... 1*074 



100*000 



The specific gravity was found to be 2*344. If 

 the proportion of iron to nickel be taken, in lOO 

 parts it is found to be 



Iron 87*84 



Nickel . 12*16 



ioo*oo 

 Zenite contains 



Iron ....••.. 85*00 

 Nickel i4"oo 



99 ■ 00 



A notable feature revealed by the analyses was the 

 similarity of the composition of the dust collected 

 from various localities and at different epochs. Thus 

 the specific gravity of fifty specimens collected within 

 such wide limits as Genoa, Palermo, Padua," Syra- 

 cuse, Naples, and Potenza, varied from 2*31 to 2*71 ; 

 the organic matter from 19*76 to 22 'oo, the oxide of 

 calcium from 4*92 to 6'00, and the silica from 47*90 

 to 53'i4. From this Macagno and Tacchini are led 

 to observe in an emphasised paragraph: ^' Quesfo 

 fatto, inentrc ci induce ad ammcttcre costante Porigine 

 di qucste polvcri, potrh forse portare qualche luce sulla 

 storia delle correnti aeree che le hanno trasportate.'" 



A microscopic analysis revealed the presence of 

 transparent and opaque polygonal crystals, black 

 granules of metallic iron, and of magnetic oxide of 

 iron, feldspar, carbonate of calcium and sand, 

 various vegetable substances and spores were ob- 

 served, Palmclla cruenta, Proto:occus nivalis \.plu- 

 vialis, and Discercea purpurea. 



Professor Tacchini considers that the dust is of ter- 

 restrial origin, and that it is brought from the Sahara, 

 being raised into the higher regions of the atmosphere 

 by cyclones and whirlwinds, where it may remain 

 suspended during transport for several days. A 

 barometric depression invariably accompanies the fall 

 of the dust. 



A notable deficiency of oxygen in the air was 

 observed by Macagno during the prevalence of the 

 scirocco at Palermo; Thus on March 20th, 1879, 



