March 31, 1887] 



NA TURE 



D'o 



live years ago I discovereil this, and succeeded in producing 

 plates a quarter of an inch in thickness and four inches in 

 diameter, by placing the basic silicate of soda within a dialyser, 

 which was floated on dilute sulphuric acid, I part to 20. 

 The plate of silica was formed in the floated vessel. A similar 

 result may be obtained by placing in a wide test-tube a portion of 

 basic silicate. Taking care that the upper portion of the tube 

 is quite free from adhering silicate, the dilute acid should he 

 poured on to the surface of the silicate without disturbing it. 

 .After a few hours the silica is eliminated in a crystalloid form. 



Possibly the first process may help us to understand how 

 labasheer m.iy have been deposited, while the second may 

 throw some light on the formation of raphides, carbonic or some 

 other acid being the active agent. 



16 Savile Street, Hull, March 15 Thomas Rowney 



A Method of Illustrating Combinations of Colours 



In Nati'RE, vol. iv. p. 346, there is a description by Mr. 

 .Mien, of Sheffield, of some methods of showing the combina- 

 tion of various colours on a screen. He used a biunial or " dis- 

 solving view " apparatus to produce overlapping disks of colours, 

 and also three lenses mounted close together in place of the 

 ordinary single lantern objective, and giving images of three 

 apertures in a lantern slide, close to which were pla;ed cells of 

 coloured liquids. 



His experiments suggested to me the following method, which 

 I have used for some years past, and for which only the ordinary 

 single optical lantern is required. 



A lens 10 cm. in diameter and 15 cm. focus is cut in half, 

 and the two halves are mounted in frames so as to be capable of 

 sliding past each other precisely in the same way as the divided 

 object-glass of a heliometer. The motion is given by a pinion 

 acting on racks in the same way as in the ordinary double- 

 b.arrelled air-pamp. 



In the frames which carry the semi-lenses are cut grooves in 

 which slips of coloured glass, or gelatine, or cells of coloured 

 liquids may be placed ; and the whole is fitted on the nose of 

 the lantern in pl.ice of the usual objective, a diaphragm with 

 round aperture about 3 cm. in diameter being put into the slide- 

 holder. 



Thus, when the two semi-lenses are so placed as to have their 

 principal axes coincident, they act as a single lens and form 

 one image of the aperture on the screen : but when they are 

 moved past each other by turning the pinion, two disks of light 

 are shown which can be separated entirely or made to overlap 

 to any required extent. If, then, glasses or liquids of any given 

 colours are placed in front of the semi-lenses, the compound 

 colour produced by their union can be easily shown, either 

 simultaneously with the component tints, or alone by accurately 

 superposing the disks, thus avoiding any disturbing effect of the 

 intrusion of other colours upon the eye. 



It is in this way easy to show, taking four prominent colours, 

 blue, green, yellow, and red, that blue -f yellow = white ; 

 blue -}■ red = purple ; green -f red = yellow, &c. 



In pl.ice of coloured liquids, which are " messy " and liable 

 to change, I almost always use coloured glasses, either singly or 

 superposed (cobalt-blue, for instance, cemented to "signal- 

 green " glass gives a good pure blue). Such glasses can by 

 patient and careful selection be obtained of almost any required 

 tint and intensity. H. G. Madan 



Eton College, March 26 



Ice-Per oi on the Altai Range 



It is generally assumed that in tlie .\ltai Range there are no 

 traces of so-called ice-.iges. Hitherto, however, only ridges on 

 the borders of the Altai Mountains have been examined. The 

 geological phenomena of the mid-Altaic regions are still almost 

 quite unknown. In the course of last summer it happened to 

 mo to visit some parts of the south .\ltaic regions — the Narim 

 Range in the vicinity of Altaiskaia, Stornitza, or Koton Kar.agay, 

 the neighbourhood of the Cossack settlement Oorool, then 

 the so-called Katoon's Pales with their snowy giant Belooha. 

 Subsequently I travelled in the valleys of the Belaia and Cher- 

 naia Berels, and visited the valley of the .\rassan lakes and some 

 other places. Everywhere I was struck by many and various 

 traces and remnants of a large icy cover, which has left 

 either strong glacier deposits, or abundant remains of moraines, 

 or pieces of granite covered with lines. The valleys, too, bear 

 on them the indubitable signs of glacial origin. In a word, there 

 can be no doubt as to the existence of a large ancient icy cover 

 here. Were these glaciers contemporaneous with the ice-age of 

 Europe and North America, or do they present themselves as a 

 quite independent system ? My own observations convince me 

 of their independence. The Altaic ice-period had, I think, its 

 own causes. The Altaic system of mountains is of great 

 antiquity ; and its ridges were probably much higher at one time 

 than they are now. Perhaps the whole system rose far above 

 the line of eternal snow, although at present this line is reached 

 only by some of the highest summits. It is probable, too, that in 

 those very remote times the meteorological conditions of the 

 country were far harsher than at present, because glaciers were 

 more numerous and descended lower, digging the V-shaped 

 valleys of the Katoon River, of the White and Black Berels 

 Rivers, of Chindagatooy, &c. 



The question of the periodicity of glacier-ages has again been 

 raised lately, and perhaps it is from the Altai and from the 

 Blue Alps that we may obtain the solid data for the complete 

 solution of this very important question. A. Bialoveski 



Oostkamenogorsk, November i, 1886 



A Claim of Priority 



J'ai eu recemment I'occasion de lire dans le Philosophical 

 Magazine (Aout 1886) la description tres-interessante d'un "in- 

 tegrateur spherique," combine par Mr. Frederick John Smith, 

 et qui semble etre une modification de celui du Prof. Hele-Shaw. 

 Mais I'idee premiere de ces appareils, et c'est sur quoi je dois 

 appeler votre attention, m'appartient sans doute, car dans le 

 No. 630 du journal anglais Nature (Novembre 24, l8Si) j'ai 

 donne la description d'un " Anemometrelntegrateur," fonde sur 

 le meme principe, et qui a ete plus tard cite dans le Quarterly 

 Journal of the Royal Meteorological Society (No. 43, 1882), par 

 Mr. Laughton ("Historical Sketch of Anemometry and Anemo- 

 meters "). 



La modification imagine'e par Mr. F. J. Smith, tendant a 

 supprimer ou a amoindrir, autant que possible, le moment 

 d'inerlie de la sphere, me parait excellente, surtout s'il fallait 

 transmettre des vitesses quelquepeu considerables. Mais quand 

 il s'agit simplement d'enregistrer celle du vent sur une echelle 

 moderee, je crois que la forme primitive sufiit, et, d'apres plusieurs 

 essais que j'ai faits, une bille d'ivoire roulantsur des cylindres de 

 bronze c'est ce qui donne les meilleurs resultats. 



Je vous prie. Monsieur le Directeur, de vouloir bien faire 

 constater dans votre estimable journal cette reclamation de 

 priorite, ainsi que d'agreer mes plus sinceres remerciments et 

 I'assurance de ma consideration tres-distinguee. 



Observatoire de Madrid, le 12 Mars V. Ventosa 



Oktibehite or Awaruite .' 



In the notice of the proceedings of the Geological Society of 

 London (Nature, December 23, :886, p. 190) the discoverj' in 

 New Zealand of a nickel alloy allied to oktibehite appears to be 

 claimed by Prof. Ulrich, of Dunedin. This requires explana- 

 tion, as the mineral was first determined, and named awaruite, 

 after the locality, by Mr. W. Skey, Analyst to the N.Z. Geo- 

 logical Survey Department on September 28, 1885, and 

 described by him in a paper read on October 25, 1885, and pub- 

 lished in the local papers at the time, as well as afterwards in the 

 Transactions of the N.Z. Institute, vol. xviii., issued May 1886. 

 A notice of it is also given in my twenty-first annual Museum 



