390 



NA TURE 



[August 27, 1908 



Astronomischer Jahresbeyicht. Vol. ix. Pp. xxxv + 

 653. (Berlin : Georg Reimer, 1908.) Price 21 

 marks. 



Wr are glad to direct attention to the ninth issue of 

 this very valuable compilation, which is of great 

 utility to all those who study astronomy, and by this 

 time should have found its place in every observatory. 

 The high standard has been thoroughly maintained, 

 and the fact that the present volume is made up of 

 653 pages gives some idea of the quantity of material 

 which has been dealt with. It may be mentioned, for 

 the information of those who are not familiar with the 

 previous annual volumes, that, in addition to the 

 references to all the more important astronomical 

 publications during the past year, a concise and 

 accurate abstract of each research in question is given 

 in nearly every case. 



The importance of having such an abstract is 

 obvious, for it enables the reader to become acquainted 

 at once with the pith of the work described, and saves 

 him probably much time and trouble, if he had had to 

 procure the original work from a library and found 

 that it did not contain tlie kind of information he was 

 desirous of obtaining. There is no doubt that the com- 

 pilation of such a volume as this involves strenuous 

 labour on the part of those who bring this information 

 together, and the least astronomers can do is to see 

 that such an undertaking is not brought to an end by 

 inadequate support on their side. W. J. S. L. 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications.] 



The Crystallisation of Over-cooled Water. 

 In order to show the over-cooling of water and to allow 

 the free development of its crystals, I endeavoured to intro- 

 duce in the over-cooled water a piece of ice put in a finely 

 drawn-out glass tube. The experiment, carried out the 

 first time by Mr. Michael Iwanow, gave an unexpected 

 result ; when the crystallisation reached the end of the tube, 

 an ice-crystal having the shape of a hexagonal star, and 



two parts. An over-cooling greater than to —3° — especially 

 when the end of the tube is not narrow enough — produces 

 several plates set in different azimuths, and the whole mass 

 becomes at last a mixture of differently sized crystals and 

 water, resembling the so-called "anchor-ice." 



The crystals are often a conglomeration of several stars 

 which have their planes, their principal rays, and even 

 the ramifications of higher order parallel (Fig. 3). 



When a star is broken the pieces of it rise hori- 

 zontally in the water with slight oscillations and attain in 

 such position the surface. This circumstance can explain 

 the verticality of optic axis of river- and lake-ice. 



The evolution of these artificial snow-crystals can be 

 easily projected on a screen if the vessel with over-cooled 

 water (a tumbler or an evaporating dish) be put into another 

 vessel with plane-parallel sides containing water of a 

 temperature somewhat higher than the thaw-temperature 

 of the surrounding air. Any water will serve for over- 

 cooling, but the refrigerating mixture (finely chopped ice 

 upon which is poured a strong solution of NaCl) must not 

 be too cold (from —4° to —6°), and its level must be lower 

 than the level of the water which is to be over-cooled. ' 



The projection is especially beautiful when the vessel is 

 placed between two crossed Nicols (the photographs of 

 Figs. 1-3 are taken in this way) ; on a dark ground grows 

 a star, which gradually becomes more and more white, 

 and at last — when thick enough (the thickness is generally 

 of the order of a tenth of a millimetre) — obtains the colours 

 of chromatic polarisation. It is easy to prove that these 

 crystals are optically uniaxial, the tube being turned so 

 long that the plane of a star is at right angles to the 

 rays of polarised light, the image of the star disappears. 



Precise measurements of these crystals are to be made in 

 winter, when it will be possible to prolong their fugitive 

 existence. The size of the stars depends — at a sufficient 

 over-cooling, e.g. of —2° — principally on the dimensions of 

 the vessel with over-cooled water ; I often obtained single 

 stars 8 cm. to 12 cm. broad. Boris Weinberg. 



St. Petersburg, July. 



Bright Meteors on August ig. 



On August 19 there was an unusual display of three 

 bright meteors within about five minutes. The details were 

 recorded here as under : — 



sec. Radiant 



202 + 62 ... 1-8 ... 288 + 59 



283 + 70 ... I'o ... 56 + 60 



256+I5J ... 2'0 ... 320-15 



9 40 I ... 220 + 66 



9 44 I ••• 355 + 794 

 9 45 ... 269+ 9i 



The first was one of the Draconids, the second a 

 belated Perseid, the third a 

 5 Capricornid. The Perseid was 

 well observed, and it would be 

 interesting to obtain a duplicate 

 record of it. 



W. F. Denning. 

 Bristol, August 20. 



Fig. 



very similar to the characteristic snow-crystals at this 

 point, began to grow. 



The greater the over-cooling of water the greater were 

 the abundance of ramifications and the velocity of crystal- 

 lisation. With water over-cooled to a temperature between 

 — o°-3 and — 1° I obtained small stars (Fig. i) with few 

 narrow ramifications. The over-cooling to a temperature 

 between —1° and —3° gave rise to stars with so densely 

 developed ramifications that they resembled hexagonal 

 plates (Fig. 2). The plane of stars contains the direction 

 of the end of the tube, and therefore when this end is 

 vertical a sufficiently large plate can divide the vessel in 



-MO. 2026, VOL. 78] 



Barisal Guns in Western 



Australia. 

 I H.w'E just received the follow- 

 ing note from Mr. H. L. 

 Richardson, Hillsprings Station, 

 100 miles north-east of Car- 

 narvon, on our west coast : — 

 " A peculiar incident happened here last evening 

 (June 26) about an hour after sunset. In a south-easterly 

 direction from here three reports took place high up in 

 the air, and then a rushing noise like steam escaping, last- 

 ing for a few seconds, and gradually dying away. Mr. 

 Loeffler, one of the owners of this station, was standing 

 outside with me at the time. It was a beautifully clear 

 evening, and there was nothing visible at all in that direc- 

 tion. The reports sounded like explosions of some com- 

 bustible to which there was no resistance." 



W. E. Cooke. 

 Perth Observatory, Western Australia, July 20. 



