April i 8, 1895 J 



NA TURE 



589 



ately depolished by the blasts now in use, and but a compara- 

 tively short time is required to pierce and cut apertures through 

 sheet and plate glass. Stone, marble, sla'.e, and granite are 

 just as amenable to the action of the sand-blast. Iron, steel, 

 and other metals have their surfaces easily reduced, and 

 smoothly or coarsely granulatel, according to the force and 

 abrasive powder used. It is remarkable that it is by no means 

 necessary that the abrasive be harder than the material to 

 which it is applied ; thus, hardened steel and corundum are 

 readily pierced with sand. The blast is not only in use for 

 producing a urjform granulation on sheet glass ; it is also em - 

 ployed for frQSting the babbles of iacandiscent lamp, and the 

 like ; for the decoration of glass ware, and the labelling of 

 graduated measi'es. In metal, the hird scale, so destructive to 

 cutting tools, is removed from castings and forging; by the 

 blast. On stone, slate, and granite the sand-blast is used for 

 incised carving an! inscriptions in intaglio or relief, and for deli- 

 cate drawing for lithography. A print of a child's head, exhibited 

 by Mr. Holtzapffel, was an astoniihing example of the delicacy 

 of treatment obtainable by the process. Among other purposes, 

 the blast is employed for removing fur and deposits in 

 tubes and tanks; foi cleaning off accumulations of paint and 

 dirt within iron ships . for decorating coat and other buttons ; 

 for piercing the aperures in glass ventilators ; for marking 

 pottery, and in the mmufacture of ornamental tiles ; for re- 

 facing grindstones, emtry, and corunlum wheels ; for granu- 

 lating celluloid films for photography ; and on wood, to bring 

 out the grain in relief, and, latterly, for blocks for printing. 

 These many and various applications of sand-blast processes 

 show that the art has developed in an extraordinary manner 

 since it was introduced by Ir. Tilghmann in 1S70. 



Dr. H. Wild has puJishei, in the Zapiski of the St. 

 Petersburg Academy of Scietces, a very impo.'tant investiga tion, 

 entitled "New Normal Ar-Temperaturei for the Russian 

 Empire." In a former paps: upon this subject, the data for 

 the monthly, yearly, and fivi-;parly means were brojght dow n 

 to the year 1875, while in theoresent work observations ha ve 

 been included to the year iSgo.md comprise materials from no 

 less than 575 station;, of which 44 are n;w. 



The additions to the Zoologies Society's Gardens during the 

 past week include an Irish Stoa (Putorius hibernicus) from 

 Ireland, presented by Viscoant bwerscourt ; a Grey "arrot 

 (Psillacus erilhactis) from West Afr;a, presented by Mr. A. A. 

 Dowty; a Cape Viper {Caiisits rhotJjiatus) from South ;Africa, 

 presented by Mr. J. E. Matcham ; ho Elephantine Tortoises 

 (lestuJo eUphantina) from the Aldbra Islands, Seychelles ; 

 four Indian Pythons {Python moltirui from India, .deposited ; 

 a Barbary Wild Sieep (Ovis traglaphus), born in the 

 Gardens. 

 . \ 



OUR ASTRONOMICAL \OLUMN. 



Lunar River Beds and Variable pots.— The highly 

 favourable atmospheric conditions at Artuipa have enabled 

 Prof. W. H. Pickering to make numerous,bservations which 

 have a special bearing on the question of th<existence of water 

 on the moon (Annals Han'ard College Ohenatory, vol. xxxii. 

 part l). In addition to the ordinary rills, P.f. Pickering has 

 catalogued thirty-five narrower ones, which, f.in their resemb- 

 lance to terrestrial watercourses, he does not «sitate to regard 

 as "river beds." These are wider at one id than at the 

 other, and the wide end always terminates iia pear-shaped 

 craterlet. Most of them are only a few miles ijength, and a 

 few hundred feet in width at the widest part, am except when 

 very deep, they are very difficult objects. Th largest and 

 most readily observed has its origin in the Mount'adley range 

 n the Apennines ; its course lies a little north of est, and its 

 otal length is about sixty-five miles. There does n appear to 



NO. 1329, VOL. 51] 



be any reason to suppose that these formations actually contain 

 water at the present time, but Prof. Pickering brings forward 

 other evidence in favour of the presence of a small amount of 

 moisture on the lunar surface. 



Certain variable dark spots have been detected in different 

 regions, many of them lying inside craters, others symmetrically 

 surrounding craterlets, and others in the dark marja, or "seas." 

 In the central craters, such as Alphonsus, the spots are darkest 

 just after full moon, when shadows are geometrically impossible, 

 and they are invisible when the shadows are stronge>t. "If 

 called upon to offer an explanation of the phenomenon, we 

 seem forced to call in the aid of water as an active agent." 

 Still, the dark spots cannot be simply ponds, as one of the 

 spots in Alphonsus for a portion of the time covers and darkens 

 the slopes of a small hill near the crater-wall. " This seems 

 to effectually overthrow the hypothesis of a free liquid surface, 

 as well as the suggestion that the dark colouration may be due 

 to frozen ground that has partially thawed. . . . Vegetation 

 would undoubtedly explain away all our difficulties ; but before 

 we resort to such an extremily, it is evident that we need more 

 facts upon which to base our theories." 



The Mare Tranquilitatis is said to be almost covered by these 

 variable spots, and Prof. Pickering stales that the changes may 

 be seen with the smallest telescope, or even with the naked 

 eye ; until past first quarter this area is lighter than the Mare 



; Crisium ; it then rapidly becomes the darker of the two until 



i after full moon, when it again becomes lighter. 



> The changes in some of the spots are readily seen in the 

 beautiful photographs which illustrate the memoir. 



The Ultka-Violet Spectrum of the Corona.— With 

 spectroscopes in which the optical parts are made ol glass, it is 

 only possible to photograph the spectrum in the ultra-violet as 

 far as wave-length 360 ; but when the spectroscopic train con- 

 sists of quartz and Iceland spar, a more refrangible region is 

 open to investigation. One of the spectroscopes employed in 

 Africa by M. Deslandres during the I 'al eclipse of the sun on 

 April 16, 1893, was of the latter form, and a plate exposed for 

 four minutes gives for the first time some information as to the 

 coronal spectrum in tlie extreme ultra-violet (Cf/«//« rendus, 

 April l). The slit of the spectroscope cut the image of the 

 corona along the equatorial diameter, and to facilitate the reduc- 

 tion of wave-lengths, the spark-spectrum of iron was photo- 

 graphed on the same plate. The photograph shows the spec- 

 trum of the corona to consist of bright lines superposed on a 

 continuous spectnim. In the blue, the continuous spectrum 

 reaches a height equal to two-thirds the sun's diameter, but it 

 diminishes both in height and intensity until about A 300 it is 

 almost reduced to zero. Forty lines are tabulated from \ 308 

 to A 362 ; one at A 31709 appears to reach a great height in 

 the solar atmosphere, and others at A 3164-5, 3189-5, and 

 3237-1, are comparable with the hydrogen lines Hj, H,, and 

 Hj. The remaining lines may belong either to the chromo- 

 sphere or corona ; but M. Deslandres considers the fact that they 

 are shown with a small image on the slit, to be in favour of 

 the view that they are coronal. Most of the lines cannot be 

 identified with known substances, and they probably represent 

 gases of low atomic weight. 



Stellar Parallaxes.— A very suggestive investigation of 

 stellar parallaxes in relation to magnitudes and proper motions, 

 has been carried out by Mr. T. Lewis (Observatory, April). 

 The parallaxes adopted are the means of the values obtained 

 by various observers, and from these the velocities across the 

 line of sight have been derived by dividing the proper motions 

 by the parallaxes and reducing to miles per second. The con- 

 clusions suggested by the tables given are : " U) Leaving out a 

 few of the brightest stars, the parallaxes are constant down to 

 2-7 magnitude. (2) After 27 mag. is reached, the parallaxes 

 are doubled and remain practically constant to 8 4 mag. (3) Up 

 to the 3rd mag. the velocities are very small, averaging 

 about 9 miles per second, while after the 3rd mag. the velocity 

 is 38 miles per second." It seems probable that in our 

 immediate neighbourhood there are a few stars of exceptional 

 brilliancy (about 8) and a few smaller stars, of which nearly 40 

 are at present known ; while stars of mag. I to 3 are as a class 

 far outside this inner space, and have very small velocities. 

 The investigation confirms the accepted idea that a measurable 

 parallax accompanies a large proper motion, and shows, further, 

 that this holds good whatever the magnitude of the star 

 may be. 



