Nov. 27, 1879] 



NATURE 



85 



tolerably wide at F and G, and which gradually dimi- 

 nishes in width towards H, and finally becomes linear 

 at M. Now as the effect of atmospheric absorption on 

 the spectrum increases as you pass from G toward H and 

 above H, by diminishing' the width of the spectrum you 

 can in some measure neutralise the effect, and at one 

 exposuie obtain a photograph of nearly uniform intensity 

 from end to end, though it is of variable width. If it 

 were not for this it would be necessary to have the spec- 

 trum over-exposed at G in order to be visible above H, 

 or else to resort to an elaborate diaphraghming which is 

 difficult. 



It is my intention next season to return to the use of 

 the 28-inch reflector, because it collects nearly five times 

 as much light as the 12-inch does, after making allowance 

 for the secondary mirror. Of course in a large reflector 

 the difficulties of flexure and instability of the optical 

 axis are much increased, and keeping a star on the slit 

 will be troublesome, especially as the magnifying power 

 on the image is about 50. 



As to the results obtained, it has already been men- 

 tioned that the spectra of several stars and planets have 

 been photographed. The subject of planetary spectra will 

 be reserved for a future communication. A preliminary 

 examination at once shows that these stellar spectra are 

 divisible into two groups : (1) those closely resembling 

 the solar spectrum, and (2) those in which there are rela- 

 tively but few lines, and those of great breadth and in- 

 tensity. The photographs of the spectra of Arcturus and 

 Capella are so similar to the solar spectrum, that I have 

 not up to the present detected any material differences. 

 But, on the other hand, the spectra of Vega and a Aquilas 

 are totally different, and it is not easy without prolonged 

 study and the assistance of laboratory experiments to 

 interpret the results, and even then it will be necessary 

 to speak with diffidence. I have not as yet obtained any 

 stellar spectrum photographs belonging to the third and 

 fourth groups of stellar spectra as described by Secchi. 

 These, if obtainable, will aid materially in discussing the 

 whole subject, but unless a star passes near the zenith it 

 is hard to make a fair study of its spectrum by photo- 

 graphy, because atmospheric absorption in the ultra-violet 

 region increases rapidly as the altitude decreases. In the 

 case of the sun I have found that at sunset the exposure 

 necessary to photograph the spectrum above H, is often 

 200 times as long as at mid-day. 



In the case of the spectrum of Vega, when examined 

 by the eye, the lines C, F, near G and //, are readily 

 visible, but lines such as D and b are relatively faint. It 

 is clear, then, that hydrogen exists to a large extent in 

 the atmosphere of that star. But on examining the pho- 

 tograph of its spectrum it is evident that other lines just 

 as conspicuous as the hydrogen lines, are present. One 

 of these corresponds in position and character to H l7 and 

 seems to coincide with a calcium line. It appears to 

 me, however, that the evidence of this coincidence is not 

 complete. 



In attempting to reason from these photographs as the 

 matter now stands, it is necessary to try at every step 

 farther experiments in order to find out whether the facts 

 agree with the hypothesis, and it is this very condition of 

 affairs that gives hopes of results valuable in their bearing 

 on terrestrial chemistry and physics. In the photographs 

 of the spectrum of Vega there are eleven lines, only two 

 of which are certainly accounted for, two more may be 

 calcium, the remaining seven, though bearing a most 

 suspicious resemblance to the hydrogen lines in their 

 general characters, are as yet not identified. It would be 

 worth while to subject hydrogen to a more intense 

 incandescence than any yet attained, to see whether in 

 photographs of its spectrum under those circumstances 

 any trace of these lines, which extend to wave-length 

 3700, could be found. 



It is to be hoped that before long we may be able to 



nvestigate photographically the spectra of the gaseous 

 nebulae, for in them the most elementary condition of 

 matter and the simplest spectra are doubtless found. 



THE FUNCTION OF CHLOROPHYLL 

 HTHE Report of the Berlin Academy for July last con- 

 ■*■ tains a remarkable paper by Prof. Pringsheim 

 on this subject. In pursuing his researches upon chloro- 

 phyll, he had found that positive results could only be 

 obtained by employing intense light, and in this paper he 

 gives some account of the conclusions at which he has 

 been enabled to arrive by the use of this method. 



By means of a heliostat and a strong lens, the object to 

 be observed under the microscope is brightly and con- 

 stantly illuminated ; the effects of this illumination, which 

 are striking, are produced in a few (3-6) minutes. As- 

 suming that the object contains chlorophyll-corpuscles, 

 the first visible effect is the rapid disappearance of the 

 green colour, so that the object appears as if it had been 

 lying for some days in alcohol, the corpuscles retaining 

 however their form and consistence. Changes now 

 gradually become apparent in the protoplasmic cell- 

 contents ; the circulation of the protoplasm, where it exists, 

 is arreted ; the bridles of protoplasm rupture, and the 

 nucleus is displaced ; the ectoplasm contracts, becomes 

 permeable to colouring-matters, and the turgidity of the 

 cell disappears ; the cell presents, in fact, all the symptoms 

 of death. 



It seems natural to suggest that these effects may be 

 due, to some extent at least, to the action of the high 

 temperature to which the cell is exposed under these con- 

 ditions. Prof. Pringsheim, anticipating this criticism, 

 is careful to point out that they are produced by all the 

 different parts of the visible spectrum. They are quite 

 evident when the light has previously passed through a 

 solution of iodine in carbon disulphide, but they are more 

 distinct when the light has passed through an ammoniacal 

 solution of cupric oxide ; the light to which the object 

 is exposed consisting, in the former case, of red rays, 

 in the latter, of blue and violet. Moreover, if the 

 solution of iodine be so concentrated that only the rays 

 of a greater wave-length than 000061 m.m. can pass, 

 these effects are not produced although about eighty per 

 cent, of the heat is transmitted ; on the other hand, if the 

 ammoniacal solution of cupric oxide be so concentrated 

 that the whole of the rays of low refrangibility to a wave- 

 length of 0-0005 1 rn- 111 - are absorbed, the effects are rapidly 

 and vividly produced, although the amount of heat which 

 passes is comparatively small. From these facts he con- 

 cludes that the phenomena in question are the results not 

 of the action of heat, but of that of light. 



This important point being settled, he proceeds to 

 determine in what manner this action of the intense light 

 is affected by the atmosphere in which the object exists. 

 As the result of a variety of experiments he finds that 

 these effects are only produced when the atmosphere 

 contains oxygen. 



These are very briefly the facts which Prof. Pringsheim 

 has ascertained by this method ; we will at once pass to 

 the consideration of the conclusions which he draws from 

 them. He concludes, in the first place, that the decom- 

 position (oxidation) of chlorophyll in the living plant is a 

 process of combustion which is influenced and promoted 

 by the action of light, and which stands in no relation to 

 the decomposition of carbonic acid by the plant. Since 

 the green colour of the chlorophyll-corpuscles which have 

 become blanched is not subsequently restored, even 

 though the cell continue to live, it appears that this 

 oxidation of the chlorophyll is not a normal physiological 

 occurrence, but that it is purely pathological. Prof. Prings- 

 heim was unable to find any substance in the cells 

 which might be regarded as the product of the oxidation 

 of the chlorophvll, neither could he detect any increase 



