May. IQll. 



KNOWLEDGE. 



189 



lying in The Minch. between Skye and the Torridon district of 

 the Ross-shire mainland, was announced late in the past year. 

 The discovery was really made eighteen years ago by Mr. 

 H. B. Woodward, F.K.S., in the course of his work on the 

 Geological Survey, but the deposit has been recently 

 investigated from a commercial point of view, and as a result 

 the great firm of ironmasters and colliery owners, Messrs. 

 ^\'m. Baird & Co., Ltd.. of the Glasgow Coalfield, have bought 

 the island. The deposit is situated at the junction of the 

 Upper and Middle Lias, thus corresponding approximately 

 with the position of the Cleveland ironstone. It is a 

 ferruginous limestone forming a good basic ore. The deposit 

 is from six to seventeen feet in thickness and probably many 

 millions of tons will be available. Though it is not likely 

 that blast furnaces will be erected on the island, for the ore 

 will merely be calcined and then shipped to the South, still 

 the opening up of mining operations in this quiet and remote 

 spot will greatly alter the character of this district of grouse 

 moor and deer forest. 



This will not, however, be the only mineral industry carried 

 on in that part of the Western Isles, for at two places on the 

 adjacent coast of Skye, quarrying has been in operation on a 

 comparatively small scale. The deposits of diatomite. a lake 

 deposit consisting of the siliceous tests of minute plants, have 

 been worked for many years in a wild, desert region north of 

 Portree, and the calcined product shipped away for use in a 

 multitude of industries — the manufacture of fireproof partitions, 

 ot tooth powder, of dynamite, of disinfectants, and so on. A 

 beautiful white marble, somewhat like the Carrara stone, and 

 produced by the metamorphic action of granite on Cambrian 

 limestone, has been ijuarried intermittently near Broadford, and 

 within the last four or five years systematic operations have 

 been carried on, a mineral railway is now being constructed, 

 and an export trade is being opened up. 



THE P.ASS.AGE OF LIGHT THROUGH CRVST.ALS. 

 — The issue of Dr. Tutton's popular account of the fascinating 

 phenomena of crystallography ("'Crystals." International 

 Scientific Series, 1911), recalls his evening discourses before 

 the British .Association in Winnipeg, and the Royal Institution 

 in London. 



I had the good fortune to be present at the Royal Institu- 

 tion lecture, and shall never forget the wonderful experiments 

 then performed. The most "showy" demonstration was an 

 illustration of the fact that the light reaching the eye from a 

 crystal is of two kinds, namely, white light reflected from 

 the exterior faces and coloured light which has penetrated the 

 crystal substance and emei'ges refracted and dispersed as 

 spectra. Two powerful beams of light from a pair of widely 

 separated electric lanterns were concentrated on a cluster 

 of magnificent large diamonds arranged in the shape of a 

 crown. The effect was not only to produce a bla^e of colour 

 about the diamonds themselves, but also to project upon the 

 ceiling of the lecture theatre numerous images in white light 

 of the poles of the electric arc, derived by reflection, 

 interspersed with coloured spectra derived from the rays 

 which had penetrated the diamonds and had suffered refrac- 

 tion and internal reflection. 



The " Mitscherlich experiment." with gypsum, was also per- 

 formed by Dr. Tutton. In this, a suitably-cut section of the 

 mineral is shown with convergent polarised light, the resulting 

 interference figure being projected on to a screen. .\t the 

 ordinary temperature, the mineral is biaxial with a wide optic 

 axial angle. .As the crystal is heated gently this angle 

 decreases, then closes up altogether (so that the mineral 

 becomes uniaxial) and finally opens out again in a plane at 

 right angles to the original optic axial plane. On allowing the 

 crystal section to cool again the phenomena are repeated in 

 the reverse order. No other mineral exhibits this phenomenon 

 of crossed-axial-plane dispersion, by change of temperature 

 alone, quite so well as gypsum. When one appreciated the 

 significance of the interference figure as projected on the 

 lecture-screen, admiration was called forth as there appeared 

 first the usual lemniscates and rings around the two optic axes 



at the right and left margins of the field; then the axes 

 approached one another and united ia the centre of the field, 

 the dark hyperbolic brushes combining to produce a 

 rectangular cross, and the rings and i'liiniscates becoming 

 circles: then the dark cross opened era .jsr.in into brushes, 

 but in the vertical direction, and the circl. s elongated out into 

 ellipses and lemniscates again. Dr. Tutton's book deals with 

 many other interesting crystallographic topics, such as the 

 significance of isomorphism and dimorphisiu, the phenomena 

 of " right- and left-handedness " in crystals, those peculiar 

 optically-active liquids described as " li(|uid-crystais " and so 

 on. 



METEOROLOGY. 



By John A. Curtis, F.R.Mf.t.Soc. 



The weather of the week ended March 18th, as epitomised 

 in the Weekly Weather Report issued by the Meteorological 

 Office, was generally cold, wet and dull, with snow at many 

 stations. Temperature was below the average in all districts. 



Readings above 50' were reported only at Tottenham, 

 .Armagh, Killarney, and in the English Channel, the highest 

 being 54 at Killarney and at Guernsey. The lowest miuinuuu 

 was 22 at Llangammarch Wells on the 1 7th, but readings below 

 freezing-point were observed in all districts. The minimum 

 on the grass was as low as 11" at Llangammarch Wells, and 18" 

 at Plymouth. Rainfall was in excess, except in the North and 

 West of Scotland, England N.W., and in Ireland; in some 

 places the amounts collected were from three to four times as 

 great as usual. The highest total reported was 1-93 inches ;it 

 Hillington. Norfolk. Sunshine was in excess in Scotland and 

 Ireland, but was generally in defect elsewhere. The sunniest 

 station was Castlebay. Harra Island, with 51-9 hours (65%), 

 while Deerness, still further to the North, but to the East, had 

 only Z-i hours (3%), Glasgow reported 28-7 hours (36%), 

 while Eastbourne had only 17-9 hours (22%). The total 

 duration of sunshine at Westminster was 9-1 hours (11%). 

 The temperature of the sea-water varied from 48° at Seafield, 

 to 37° at Cromarty. .A thunderstorm was reported at 

 Rothamsted and Raunds on the 13th: at the latter station it 

 was accompanied by a violent snowstorm and great darkness. 



The week ended March 25th was cool and unsettled, with 

 snow in many places, and with thunderstorms in the S.E. and 

 S. Temperature was above the average in England S.E. and 

 in the English Channel, but was below the average elsewhere. 

 The highest readings recorded were 63" at Tottenham on 

 the 22nd, and 62° at Margate and at Guernsey. The lowest 

 of the minima were 22^ at Fort .Augustus and at Balmoral. 

 On the grass the minimum fell to 18^ at Balmoral and to 19° 

 at Llanganunarch Wells. Rainfall was light as a rule, and in 

 Scotland W. and Ireland N. the week was rainless. In 

 Scotland N. the total district value was only 0-03 inch, or 1-00 

 inch below the average for the week ; in England N.W. the 

 amount was 0-04 inch, or 0-49 inch less than usual. Bright 

 sunshine varied much in different localities, but was generally 

 below the normal. Castlebay was again the sunniest station, 

 with 54- 7 hours (65%), Worthing coming next with 50-9 hours 

 (61%). Sheffield had only 9-0 hours (11%): Westminster 

 reported 19-9 hours (24%). The mean temperature of the sea 

 ranged from 37-5 at Cromarty to 47" -0 at Newquay. 



The week ended April 1st. was dry, though cool and cloudy, 

 but heavy rain commenced in the S.E. of England late on 

 Saturday. Temperature was in excess in Scotland N. and 

 England N.W., but was in defect in all other districts. 

 The highest maximum reported was 63° at Arlington, N. 

 De\on, on the the 30th, but in most of the districts the 

 thermometer did not rise as high as 60°, and in England N.E. 

 the maximum was only 51°, and at individual stations it was as 

 low as 45". The lowest readings for the week were 22" at 

 Balmoral, and at Markree Castle, and 23° at Cromer. The 

 minimum on the grass was 15° at Markree Castle. 



Rainfall was below the average everywhere except in England 



