52 



KNOWLEDGE. 



[March 1. 1893. 



The illustration of scientific lectures or papers by means 

 of lantern slides is becoming fairly general, and it certainly 

 tends to render the meetings of learned societies more 

 instructive as well as more interesting. In this way the 

 physical features of a country, or the microscopic structure 

 of a rock, the organisms of sewage, or the " extinct 

 monsters " of many geological periods, may be reproduced 

 on the screen from photographs or original drawings. The 

 Astronomical Society, the Eoyal Society, the Linnaaan 

 Society, the Eoyal and the London Institutions, the 

 Geologists' Association, and probably other bodies in 

 Loudon, have introduced the lantern into their meeting 

 rooms with marked success ; the Geological Society, 

 however, has hitherto held aloof. 



It has been asserted that anomalous disturbances of 

 magnetic needles have occurred when brilliant faculs were 

 visible near the middle of the sun's disc ; and the conclusion 

 jumped at was that the two phenomena were intimately 

 connected. In the Cowptes Bendux of February (jth, Prof. 

 George Hale deals with this theory. Photographs of the 

 sun have been taken with the spectro-heliograph of 

 Kenwood Observatory since the beginning of last year. 

 Of the 142 pictures obtained, 132 show one or more 

 groups of facula; on or near the central meridian of the 

 solar disc. It would therefore have been ditlicult to find 

 an unusual movement of the magnetic needle which did nut 

 coincide witli the appearance of faciilio near to the middle 

 of the sun's disc. 



Prof. Crookes and others have for some years been making 

 experiments which go to prove that the so-called elements 

 have not the absolutely fixed atomic weights generally 

 assigned to them, or that there exist a great number of 

 unrecognized substances shading off by almost imperceptible 

 differences from one element towards another. The latest 

 experiment is that of Lord Rayleigh, who has prepared i 

 nitrogen by two different methods, and finds the atomic 

 weight of one specimen to be one-thousandth part less than 

 that of the other. | 



By the reflecting power of a surface is meant the ratio | 

 of the amount of light reflected by it to the total amount 

 of hght incident upon it. Zollner and others have deter- 

 mined this ratio for various substances, and also for the 

 planets and some of their satellites. Dr. Sumpner has 

 I'ecently made a number of similar measures of the 

 reflecting powers of common materials. He finds that 

 white blotting paper reflects 82 per cent, of the incident 

 light ; white cartridge paper, 80 per cent. ; tracing cloth, 

 35 per cent. ; ordinary foolscap, 70 per cent. ; deep 

 chocolate paper, 4 per cent. ; and black velvet, only 0'4 per 

 cent. 



We are glad to notice (says Natural Science) that the 

 New Zealand Government is actively engaged in preventing 

 the total extinction of the rarer plants and animals of the 

 colony. Acting on the advice of Mr. Henry Wright, the 

 Government has arranged for the purchase of Little 

 Barrier, or Hiuturu Island, near Auckland, which will be 

 kept as a national preserve. This island measures 4 J 

 miles in length by 3j miles in breadth, and rises in the 

 centre to au elevation of 2000 feet. It is generally rugged, 

 but there is comparatively flat land at the northern and 

 southern extremities. Even now its flora and fauna are 

 particularly rich and varied, and no more suitable area 

 could have been secured. 



The engineer of the Channel Tunnel Company makes 

 the following statement in his recent report of the trial 

 boring for coal — " The coal boring has now reached a 

 depth of 2228 feet, including- 1071 feet of coal measures 

 in which nine workable seams have been foimd, containing 

 altogether 20 feet in thickness of good bituminous coal. 

 This coal is suitable for gas making and household 

 purposes. The deepest seam, 4 feet in thickness, was met 

 with at 2222 feet from the surface." 



A series of very interesting photographs has been made 

 illustrating the movements of the growing parts of such 

 climbing plants as the convolvulus and the hop plant. It 

 is said that the " movement of the young stems consists of 

 a succession of irregular circular or elliptical curves which 

 vary every moment, even in their direction." This succes- 

 sive series of photographic records reveals some interesting 

 facts. For instance, it is found that, even when they are 

 asleep, plants move continuously, and not intermittently, 

 as was formerly supposed. 



Mr. Edmund G. Gardner, of Cambridge, contributes to 

 Nature (.Tan. 26th; a most interesting article on Dante's 

 " Inquiry concerning Water and Land." The treatise is 

 little known in comparison with the other writmgs of the 

 poet, but its genuineness and importance are now almost 

 universally admitted. It seems to have been his last work, 

 and has not yet been translated into English. According 

 to this work, a good deal of so-called modern science was 

 anticipated by the great Italian poet. Mr. Gardner con- 

 cludes by giving a list of nine scientific truths about the 

 earth known to Dante, amongst which are (1) the moon, 

 the principal cause of tides ; (2) equality of the sea's level ; 

 (3) " centripetal force " ; (4) sphericity of the earth ; (5) 

 northern grouping of the continents ; (6) universal attrac- 

 tion ; (7) elasticity of vapours as a motive power. The 

 reader is referred to Signor A. Stopani ("La questione dell' 

 Acqua e della Terra di Dante Alighieri," in " 0pp. Lat. 

 di Dante," ed Guiliani, Vol. II.). 



A large audience assembled at the Royal Institution on 

 February 21st, to hear Prof. Dewar lecture' on " Liquid 

 Air." Until recently, liquid oxygen was a curiosity, only 

 produced in very small quantities — too small and too 

 evanescent to admit of any exact examination of its 

 properties. Prof. Dewar produces it by the pint, and 

 demonstrated its more obvious physical properties — its 

 beautiful blue colour, somewhat like the blue of the sky, 

 its high magnetic quality, and its characteristic spectrum — 

 with as much facility as if he had been dealing with water. 

 He surrounds the vessel containing the liquid with a high 

 vacuum, in order to reduce the flow of heat, by convection, 

 not by radiation, as was suggested in the Times. Liquid 

 air behaves in the magnetic field and in the spectro- 

 scope simply as diluted oxygen. When the liquid is allowed 

 to boil, the nitrogen distils off first (having a lower boiling 

 point), and the oxygen follows. 



Dr. Gilbert, of the U.S. Geological Survey, communi- 

 cated a quaint paper on the origin of lunar craters to the 

 National Academy of Science, in November, 1892. His 

 theory is based upon the phenomena of the planet Saturn 

 and its ring. "Assume,'" says Dr. Gilbert, "that a 

 similar ring of minute satellites once encircled the 

 earth, and that these gradually became aggregated into a 

 smaller number of larger satellites, and eventually into a 

 single satellite — the inoon. Tlie craters mark the spots 

 where the last of the small bodies collided with the surface. 



