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NA TURE 



[May 25, 1893 



are not debarred from making use of any available infor- 

 mation, published or otherwise, on the subject. A photo- 

 graph of each "burster " described, giving a characteristic view 

 of the cloud roll should, if possible, be sent with the essay. 



Dr. N. Wills has been appointed ordinary professor of 

 1 otany at the University and Director of the Botanic Gardens at 

 Chrisliania. 



A MOST disastrous landslip occurred on the night of 

 May l8, at Vaerdalen, in the district of North Trondhjem. 

 Vaerdalen is a straggling country town with about 6000 

 inhabitants, and is an agricultural centre. The landslip occurred 

 in the outskirts of the town, where there are a number of houses 

 occupied by peasants, each farming his own land. The subsi- 

 dence was so sudden and severe that between thirty and forly 

 of these farmhouses fell instantaneously in ruins, leaving 

 scarcely a wall standing. Twenty-two of the demolished houses 

 were of considerable size, and many people were asleep in them 

 when the catastrophe happened. The number of victims is 

 estimated at close upon one hundred. The loss of property ii 

 very great. According to a Renter's telegram, from which we 

 learn these details, the most fruitful part of the Vaerdals-Elv 

 Valley lies under a mass of mud and slime, and it is feared that 

 further landslips will occur. 



During the past week the day temperatures over the British 

 Islands have been mostly below 70° in the south and west, while 

 in the north of Scotland several of the maximum readings have 

 not exceeded 55°. On the l8th inst. rainy weather had become 

 general, with thunderstorms in many places ; on that morning 

 some heavy falls were measured, Ardrossan reporting 075 inch, 

 York 074 inch, Loughborough r6u inch, and Jersey o'gi inch, 

 while on the following days large amounts were measured in 

 various parts of Ireland. A small depression lying off the 

 south-east coast of England on Sundaj-, the 21st inst., also 

 brought over half an inch of rain to that part of the country, 

 while in the early part of the present week the distribution of 

 atmospheric pressure was favour-able for further falls over the 

 country generally. The Weekly Weather Keport of the 20th 

 inst. showed that the excess of temperature for that week ranged 

 from 4° in the northern districts to 6° in most parts of England, 

 that the rainfall was rather less than the mean in the north of 

 Scotland, and equalled, or exceeded it, in all other districts. 

 From the beginning of the year there is a deficit in all districts, 

 amounting to 5-3 inches in the west of Scotland. Bright sun- 

 shine was below the average amount in all districts. 



A PAPER on " Wreck-raising in the River Thames " was read 

 by Mr. C. J. More, engineer to the Thames Conservators, at 

 the meeting of the Institution of Civil Engineers on May 16. 

 Mr. More mentioned that during the past eleven years seventy- 

 four .steamers of 55,758 tons register, fifty-four sailing vessels of 

 9,128 tons, and three hundred and one barges of 11,956 tons, 

 being a total of 76,842 ton's register of shipping, had been 

 raised by the Conservancy lighters. 



The death of the well-known engineer, Mr. E. A. Cowper, 

 is announced. He was in his seventy-fourth year. Mr. Cowper 

 displayed much ingenuity as an inventor, and was connected 

 with many technical institutions, including the Institution of 

 Civil Engineers, of the council of which he was a member, the 

 Institution of Mechanical Engineers, of which he was president 

 in 18S0-81, and the Iron and Steel Institute. 



A MAP of the smokes of Paris has been recently prepared by 



M. Eoubert, of the Tour Saint Jacques. The idea is to note 



the position of the principal factory chimneys, to observe 



during the day the emission of smoke, then to indicate 



NO. 1230, VOL. 4-8] 



on the map, for each chimney, by means of circles of various 

 sizes and tints, the extent of the nuisance. There are obvious 

 defects (as M. Delahaye points out in the Reiiue IndustrielU) 

 in such a mode of representation. Thus no account is taken of 

 smoke from the environs, which materially affects Parisian air. 

 The black particles emitted from factory chimneys in some 

 cases sink rapidly, but in others are long maintained in suspen- 

 sion. Then there is the large emission of smoke from private 

 dwellings. M. Delahaye manifests some partiality for city 

 smoke ; he remarks on its antiseptic properties in time of 

 epidemic, and on the screening action, whereby it prevents 

 losses of heat by radiation. 



At the meeting of the Linnean Society of New South Wales 

 on March 29 Prof. David contributed a note on the discovery by 

 hiuaof the mineral sphene in situ in granite at the Bathurst water- 

 works. In the latest edition of his work on the minerals of 

 New South Wales, Prof. Liversidge has described a single well- 

 formed crystal of sphene from New South Wales, but the exact 

 locality from which it came is uncertain. In the Bathurst granite 

 crystals of sphene are abundant, and vary in size from 7,'jth up 

 to \ inch in longest diameter. The crystals are of a very deep 

 brown colour, and feebly translucent. In chemical composition 

 the mineral is a compound of silica, lime, and titanic acid. 



M. Verner has a note in the Journal de Physique on an ex- 

 planation of the rotation of the plane of polarisation in a 

 magnetic field based on de Reusch's experiments. From the ex- 

 perimental fact that a pile of birefringent plates in which the 

 principal sections are arranged helically rotates the plane of 

 polarisation, it follows that a birefringent body turning about a 

 direction perpendicular to its optical axis will rotate the plane 

 of polarisation of a ray which traverses it parallel to the axis 

 about which it is turning. For if the body is supposed divided 

 into a series of plates by planes perpendicular to the axis of 

 rotation, while the light is traversing the first plate the body 

 will have turned through an angle, and therefore the principal 

 plane of the second plate will be inclined to the direction 

 which the principal plane of the first plate occupied when the 

 light passed through it. Thus if the speed of rotation is com- 

 parable with the velocity of light the plane of polarisation will 

 be rotated. This being so, the author makes the hypothesis 

 that, in a magnetic field, at any given moment, the magnetic 

 stress at a point on a line of force is only exerted in a certain 

 azimuth normal to the direction of the line, and that the plane 

 containing the portion of the line of force, and the direction 

 of this stress, turns about the direction of the line of force with 

 a velocity proportional to the intensity of the magnetic field at 

 the point. Hence, when a substance such as carbon bisulphide is 

 placed in a magnetic. field, this magnetic stress, transversal to 

 the lines of force, causes the body 10 become birefringent, 

 with its principal plane coinciding wiih the direction of this 

 stress, and if, as is supposed, this direction rotates, the principal 

 plane will rotate, and the substance will exhibit magnetic 

 rotatory power. The above explanation accounts for the fact 

 that the direction of the rotation is independent of the direction 

 in which the ray of light traverses the magnetic field. 



The extensive researches of Pellat have shown the con- 

 siderable change produced in the value of the diflference of 

 potential between the layers of air covering two melals in con- 

 tact by the least chemical or mechanical alteration of the 

 surfaces. In the jtournal de Physique for .May M. Goure de 

 Villemontce describes his attempts to prepare metallic surfaces 

 which shall give a constant dilTerence. For this purpose he 

 deposits the metal by electrolysis on plates of copper, or 03 

 small lead shot, and has studied deposits of iron, nickel, zinc, 

 and copper made from solutions of different salts, at tempera- 



