330 



NA TURE 



[July 31, 1890 



were stopped. A sooty metallic plate at 30° to 25° held 3 to 5 

 seconds over the leaf opened the stomata, while dark heat- rays 

 of sunlight failed to do so. The stomata opened also on passing 

 a stream of warm, nearly saturated, air over the leaves. A 

 shaking of plants acts not by way of shock, but by changing the 

 atmosphere about the leaves, and therefore like wind. Strong 

 shaking stimulates transpiration ; while weak vibration has no 

 perceptible effect. The effect of wind was studied by directing 

 air-currents of measured strength on the plants. The action of 

 the weaker currents proved proportionally greater than that of 

 stronger. The transpiration is greater if the leaves are free to 

 be moved than if they are fixed. 



The additions to the Zoological Society's Gardens during the 

 past week include two Ravens {Corvus corax), British, presented 

 by Mr. Walter Chamberlain, F.Z. S.; two Wheatears {Saxicola 

 ananthe), two Whinchats {Pratincola rubetrd), two Great Tits 

 (Parus major), British, presented by Mr. J. Young, F.Z.S. ; a 

 Cuckoo {Cuciilus canorus), British, presented by Mr. Valentine 

 Marks ; a Black Tortoise {Tesludo carbonaria) from Jamaica, 

 presented by Master Morris Blake ; a Dwarf Chameleon {Chctma:- 

 Icon pumilis) from South Africa, presented by Mr. H. Tholen ; 

 a Brazilian Hangnest {Icterus janiaicai), two Bluish Finches 

 {Spermophila ccerulescens), a Tropical Seed- Finch {Oryzoborus 

 torridus), a Thick-billed Seed-Finch {Oryzoborus C7-assirostris) 

 from Brazil, a Black-faced Kangaroo {Macropus melanops i ) 

 from South Australia, deposited; a Thar {Capra jemlaica ? ), 

 two Mule TiQzx {Cariacus macrotis ? ? ), five Cuming's Octodons 

 KOctodon ctiiningi), born in the Gardens. 



OUR ASTRONOMICAL COLUMN. 

 Objects for the Spectroscope. 



Sidereal Time at Greenwich at 10 p.m. on July 31 

 i8h. 37m. 53s, 



Remarks. 



(l) The well-known Ring Nebula in Lyra, which has been 

 described in great detail by various observers. The spectrum 

 consists of bright lines, but the line near X 500 is the only con- 

 spicuous one. When the image of the nebula is sharply focussed 

 on the slit, the chief line is seen as two bright dots connected 

 by a faint line, indicating that nebulous matter fills the interior 

 of the ring. (This is also confirmed by the telescopic appear- 

 ance.) The line F and the one near \ 495 are exceedingly 

 faint, but they are undoubtedly present. In my own observa- 

 tions, with a lo-inch refractor, I have also glimpsed a less 

 refrangible line, but have not been able to determine its position 

 with any degree of accuracy. Further investigation of this line 

 should be made with as large an aperture as possible. It is not 

 far from b. 



(2) D'Arrest and Dun^r agree in describing the spectrum of 

 this star as one of Group II. with well-developed bands. The 

 bands at the red end are the strongest, indicating that the star 

 is well advanced in condensation. The bands in the red are the 

 last to disappear in passing to stars like a. Tauri, and hence this 

 conclusion. As in similar stars, the line absorptions at this 

 stage afford an interesting study. We do not know yet, for 

 instance, the stage at which the hydrogen lines first appear, 

 although we now certainly know that they are present in a 

 Orionis. The same also applies to D and b. 



NO. 1083. VOL. 42] 



(3) The integrated spectra of the components of this doubK 

 star present an appearance similar to that of a well-developed 

 star of the solar type. No attempt has apparently yet been 

 made to separate the two spectra. This should be done, if 

 possible, and the usual more detailed observations as to whether 

 the temperature is increasing or decreasing should be made. 



(4) A star of Group IV. (Gothard). 



(5) According to the observations of Duner, this star has a 

 fine spectrum of Group VI., the principal bands being very wide 

 and dark. In addition to these, the secondary bands 4 and 5 

 (\ 589 and 576 respectively) were easily seen, and band 2 (A 621) 

 was also feebly visible. What is most required in this group of 

 stars is a very detailed examination with the largest possible 

 apertures. If such be undertaken, particular attention should 

 be given to the presence or absence of line absorptions. 



(6) This variable is chiefly of interest because its spectrum is 

 one of Group VI. We have as yet no knowledge, as we have 

 in the case of variables of Group II., of the variations of spec- 

 trum which accompany the increase of light at maximum. The 

 range of variation in V Corona; is very considerable — 7*5 to 12 

 in a period of about 357 days ; and it is not unlikely that well- 

 marked changes may take place in the spectrum. Duner states 

 that the carbon band near A. 56415 weaker than that near A 517, 

 and that the secondary bands are not visible ; but he gives no 

 indication of the magnitude of the star at the time of his obser- 

 vation. Prof. Lockyer's investigations appear to indicate that 

 the dark carbon bands should be proportionately less strongly 

 marked at maximum than at minimum. There will be a maxi- 

 mum about August 5. 



A. Fowler. 



Distribution of the Perihelia of Comets.— In 1880, 

 Dr. Henry Muirhead directed attention to the arrangements 

 which the perihelia of comets exhibit in relation to the sun's 

 line of flight, and pointed out that, taking the twenty-two 

 comets given in the " Encycloptedia Britannica" along with 

 thirteen others whose elements were given in Nature up to 

 the date of his communication, and arranging them according 

 to their heliocentric longitudes, the perihelia were seen to be 

 crowded into the quadrants which the sun's line of flight bisects, 

 as compared with those taking place in the quadrants flanking 

 the said line (Proceedings of the Philosophical Society of Glas- 

 gow, vol. xiii.). By examining the succeeding volumes of 

 Nature, Dr. Muirhead has obtained the heliocentric longi- 

 tudes of the perihelia of forty-one more comets, and in a com- 

 munication to the Philosophical Society of Glasgow, on February 

 5, 1890, he showed that they also exhibit the same tendency to 

 cluster near heliocentric longitudes 263° and 83° — that is, the 

 longitude of the " apex " and "quit " of the sun's way adopted 

 by him. 



It will be remembered that Mr. H. S. Monck, in a letter to 

 the Observatory, in December 1888, remarked that, in ex- 

 amining catalogues of comets, he found 177 comets with peri- 

 helia north of the ecliptic, against 115 with southern perihelia. 

 With respect to this circumstance, Mr. Monck wrote :—" Our 

 observing stations are chiefly situated in northern latitudes. 

 Comets are rarely visible when very remote from their peri- 

 helia ; therefore, comets which pass their perihelia north of the 

 ecliptic are more likely to be detected and observed than comets 

 which pass their perihelia to the south of it. . . . As the point 

 towards which the sun is moving lies to the north of the 

 ecliptic, it might be expected that more comets would, on the 

 whole, come to us from the north than from the south. But a 

 comet coming from the north will usually have its aphelion north 

 and its perihelion south. The fact that three-fifths of the comets 

 have their perihelia to the north and their aphelia to the south 

 thus becomes more significant, and I can hardly regard it as 

 wholly the result of the position of our observing stations." 



Later, however (August 1889), Dr. Holetschek drew attention 

 to a pamphlet " Ueber die Richtungen der grossen Axen der 

 Cometenbahnen, " in which he shows that " the tendency of comet 

 perihelia or aphelia to accumulate rather in small latitudes, and 

 about the longitudes 90" and 270° than in other places, can be 

 explained by purely terrestrial considerations, and, consequently, 

 this accumulation offers no proof of the motion of the solar 

 system or of the ultra-solar origin of comets." In fact, it 

 appears that the distribution in latitude of the perihelia of 

 comets is nearly uniform, and has not a marked maximum in 

 the latitudes of the sun's line of flight, although, as Dr. Muir- 

 head indicates, a clustering of aphelia and perihelia occurs 

 near the heliocentric longitude of the line. 



