November 1, 1890.] 



KNOWLEDGE 



249 



adapted to subserve the requirements of both. The 

 stomata are then, properly speaking, the ti-dnspirunj urf/anx 

 of plants. How is it they have acquired that name which 

 has furnished the headinu; to tliis article ".' Although all 

 plants which contain chlorophyll inhale during simlight 

 carbon dioxide and exhale oxygen, they nevertheless ex- 

 hibit a phenomenon the antithesis of this, namely, that of 

 respiration, the inlialation of oxygen and exhalation of 

 carbon dioxide, processes identical with those which take 

 place when an animal breathes. And just as in an animal 

 breathing must go on contmuously during its life, so the 

 phenomenon of respiration is a continuous one in plants, 

 differing in this respect from the intermittent process of 

 carbon assimilation. The Litter is so much in excess of 

 the former, however, during bright sunlight as almost to 

 completely obscure it. It is doubtless the case that the 

 carbon dioxide and oxygen which are absorbed by a plant 

 go in chiefly by way of the leaves, but that the stomata 

 are of especial importance iu this connection is open to 

 doubt; in fact, Boussingault has proved that the leaves of 

 the Poplar, Chestnut, Peach, Ac, absorb carbon dioxide 

 more readily by their upper than by their under surfaces, 

 although stomata are more numerous on the latter than 

 on the former. Unquestionnbly they afford means of exit 

 to carbon dioxide during respiration, and to oxygen during 

 carbon assimilation ; but the regulation of transpiration, 

 or exhalation of watery vapour, is the true function of 

 those organs which were held by the old botanists to be 

 all important in respiration, and hence named by them 

 the breathing organs of plants. 



COLOURED STARS. 



By .T. E. GuKE, F.R.A.S. 



ON a clear night a careful observer will notice a 

 marked difference in the colours of the brighter 

 stars. The brilUaut white or bluish white light 

 of Sirius, Rigel, and Vega contrasts strongly with 

 the yellowish colour of Capella, the deeper yellow 

 or orange of Arcturus, and the ruddy light of Aldebaran 

 and Betelgeuse. These colours are, however, limited to 

 various shades of yellow and red. No star of a decided 

 blue or green colour is known, at least among those 

 visible to the naked eye in the Northern Hemisphere. 

 The third magnitude star Beta Librre is described by Webb 

 as of a " beautiful pale green hue"; but probably such a 

 tint in the light of this star will to most people prove 

 quite imperceptible. Dr. Gould, observing it in the 

 Southern Hemisphere, says : " There is a decidedly greenish 

 tinge to the light of j3 Librse, although its colour cannot 

 properly be called conspicuous." 



Among the ruddy stars visible to the naked eye, 

 Herschel's "garnet star" Mu Cephei is generally admitted 

 to be the reddest, but it is not sufficiently bright to enable 

 its colour to be well distinguished without the aid of an 

 opera-glass. With such an instrument, however, its 

 reddish hue is striking and beautiful, and very remarkable 

 when comj)ared with other stars in its vicinity. Like so 

 many of the red stars, Mu Cephei is variable iu its light ; 

 but it seems to have no ri'guhir period, and often remains 

 lor many weeks without perco))tible change. It may be 

 seen near the zenith in the early evening hours, towards 

 the end of October, and in this position its curious 

 colour is very conspicuous. Among the brightest stars 

 Betelgeuse is perhaps the reddest ; anil the contrast 

 between its ruddy tint and the white colour of Bigel, in 

 the same constellation, is very noticeable. Like Mu 

 Cephei, Betelgeuse is irregularly variable iu its light, 



but not to such an extent, and, hke the " garnet star," it 

 frequently remains for lengthened periods nearly constant 

 in brightness. There are other cases of reddish colour 

 among the naked-eye stars. Among these may be noted 

 Antares, Alphard (^Alpha Hydrsej, noted as red by the 

 Persian astronomer Al-Suti, in the lOth centmy, and 

 called by the Chinese "The Bed Bird"; Eta and Mu 

 Geminorum, Mu and Xu Ursse Majoris, Delta and Lambda 

 Draconis, Beta Uphiuchi, Gamma Aquilae, itc, and others 

 in the Southern Hemisphere. 



But it is among the stars below the limit of naked-eye 

 vision that we meet with the finest examples of the red 

 stars. Some of these are truly wonderful objects. The 

 small star No. 592 of Birmingham's Catalogue of Bed 

 Stars (No. 713 of EspLn's edition), which lies a Uttle 

 south of the b\ magnitude star 79 Cygni, was described as 

 "splendid red" by Birmingham; "very deep red" by 

 Copeland and Dryer ; and " orange vermilion " by Franks. 

 The star Birmingham 248, which hes about 5 degrees 

 south of Nil Hydne, is another line specimen, Birming- 

 ham described it as "fine red" and "ruby"; Copeland 

 as " brown-red"; Drey er as " copper-red "; and E spin as 

 " magnificent blood -red."-' This star is variable in light, 

 as the estimates of magnitude range from 6'7 to below 9. 

 About 3 degrees to the north-east of this remarkable 

 object is another highly-colom-ed star, known as E. 

 Crateris. It is readily found, as it hes iu the same 

 telescopic held of view with Alpha Crateris, a 4^ magnitude 

 star. Sir .John Herschel described it as " scarlet, ahnost 

 blood-colour ; a most intense and curious colour." Bu'ming- 

 ham called it " crimson," and Webb " very intense ruby." 

 Observing it with a 3-iuch refractor in the Punjab in 

 1875, I noted it as " full scarlet." It varies m hght from 

 above 8th to below 9th magnitude, and has near it a star 

 of the 9th magnitude of a pale blue tint. 



Another very red star is No. 4 of Birmingham's Cata- 

 logue, which will be found about 5 degrees north pre- 

 ceding the great nebula iu Andromeda. It is of about 

 the 8th magnitude, and may be well seen with a 3-mch 

 telescope. Kriiger describes it as " intensiv roth," Bir- 

 mingham as " fine red " and " crimson, ' I'rauks as " tine 

 colour, almost vermilion," and Espin as " uitense red 

 colour, most wonderful." 



Another fine object is R. Leporis, which forms roughly 

 an equilateral triangle with Kappa and Mu Leporis. This 

 also is variable fi'oiu 6J to 8^ magnitude. It was dis- 

 covered by Mr. Hmd hi 1845, and described by him as 

 " of the most intense crimson, resembling a blood-di'op on 

 the background of the sky ; as regards depth of colour, no 

 other star visible in these latitudes could be compared 

 with it." Schonfeld calls it " intensiv blutroth " ; but 

 Duner, observing its spectrum m 1880, gives its colour as a 

 less intense red than that of other stars. Possibly it 

 may vary in colour as well as in light. 



The variable star U. Cygni, whichlies between Omicronand 

 Omega Cygni, is also very red. Webb described it as snow- 

 ing " one of the loveliest hues iu the sky." It varies fi'om 

 about 7 to 11.V magnitude with a period of about 461 days. 



Another deeply-coloured star is the well-known variable 



* The colour sensations produced by the light of the same star 

 in the eyes of different observers probably differ, and the words they 

 select to describe and compare such colours differ more widely still. 

 To my eye no star in the heavens appears nearly as red as the 

 light from a railway-signal or the port-light of a ship. The light 

 of such stars appears to my eyes as decidedly reddish, but not so 

 rod as the sparks from a locomotive as they die out, while tiiO light 

 from Vega appears to me decidedly bluish. Prof. PicRering's spectro- 

 scopic survey of the heavens will afford us a much moro detmite 

 and satisfactory means of judging as to changes in the quality of the 

 light of stars than wo have hitherto possessed. — A. C. R. 



