Jtdy 24, 1 8 79 J 



NATURE 



301 



sending me beautiful Eozoon pieces, I cannot say to 

 them : According to my investigations also Eozoon cana- 

 densc must be regarded as a fossil species of foraminifera. 

 I am convinced that both, like myself, had the honest in- 

 tention to represent correctly the true nature of Eozoon. 

 But they must own that in their descriptions they did not 

 investigate so closely nor describe so minutely the shapes 

 nor the relative positions of the various parts, as I have 

 done in my treatise. If they had done this then I believe 

 that the facts would have led them to the same conclusions 

 which they forced upon me. 



" If the Eozoon pieces from the Laurentian or ' Ur- 

 gneiss' formation were really remains of an undoubted 

 foraminifera species, then we should possess in them cer- 

 tain proofs that even during the formation of the most 

 ancient strata of the earth's crust living beings occurred, 

 and that the first organisms belonged to the lowest 

 animals, by which biology and geology would have gained 

 two highly important facts. Yet by the scientifically 

 justified elimination of Eozoon from the domain of organic 

 beings it is not proved that during the Laurentian period 

 no living beings existed. Perhaps the graphite of the 

 Urgneiss formation has its origin in organic beings. 



" The proof that Eozoon is not a fossil rhizopod will per- 

 haps for many persons take away an important link from 

 the beautiful picture of the de^'eIopment of organic life 

 upon the earth, which they may have drawn up for them- 

 selves. But the object of natural research does not con- 

 sist in finding reasons for attractive conceptions about 

 nature, but in knowing nature as it really is. Because 

 only an insight into the real condition of nature can, in 

 the long run, satisfy the scientific mind, which gives up as 

 errors the most attractive hypotheses regarding the 

 essence and action of nature, if in the face of newly dis- 

 covered facts they can no longer hold good, no matter 

 whether these erroneous hypotheses may have reigned 

 supreme for a long time previously, and may have been 

 held to be the best conceptions of nature by the most 

 eminent authorities." 



THE BLOWPIPE CONE-SPECTRUM, AND THE 

 DISTRIBUTION OF THE INTENSITY OF 

 LIGHT IN THE PRISMATIC AND DIFFRAC- 

 TION SPECTRA 



^r OW that the optical properties of the blowpipe blue 

 ■*• ' cone have been so critically investigated, may I 

 draw the attention of the readers of Nature who are 

 interested in the history of spectrum analysis, to what I 

 think are the earliest experiments on that subject. They 

 were published by me in 1848. The memoir in which 

 they are reprinted may be found in my " Scientific 

 Memoirs." It contains a woodcut of the five rays, 

 adjusted to a reference solar spectrum on page 64, and 

 another of the five images of the cone on page 69. 



Let me also refer to some experiments I have recently 

 made on the distribution of the intensity of light on the 

 spectrum, by the aid of a new form of spectrometer, 

 which depends on the well-known optical principle, that 

 a light becomes invisible when it is in presence of another 

 light about sixty-four times more brilliant. 



In a memoir I am now publishing in the American 

 Journal of Science, and which, I presume, will also 

 appear in the Philosophical Magazine, I have described 

 several moditications of this instrument. The following 

 is one easily made : — 



Remove from the common three-tubed spectroscope 

 its scale-tube, and place against the aperture into which 

 it was screwed a glass ground on both sides. In front of 

 this arrange an ordinary gas Ught attached to a flexible 

 tube, so that its distance from the ground glass may be 

 varied at pleasure. This light I call the extinguishing 

 light. On looking through the telescope-tube the field of 

 view will be found uniformly illuminated, this being the 



use of the ground glass, the light of which is reflected 

 from the prism. The brilliancy of the field depends on 

 the distance of the extinguishing light from the ground 

 glass, according to the ordinary photometric law. 



Now, if another small gas flame be set before the slit 

 of the instrument, on looking through the telescope its 

 spectrum will be seen in the midst of a field of light. If 

 the illumination of that field be made very brilliant, the 

 spectrum will be extinguished ; if feeble, all the coloured 

 regions appear. By moving the extinguishing flame to 

 proper distances, it will be found that the violet region 

 is the first to disappear, the red the last. The yellow by 

 no means resists longest, as it ought to do if it were the 

 most brilliant. Hence it follows that in the prismatic 

 spectrum, the red and not the yellow is the brightest ray. 



If the cause of the increasing intensity of light in the 

 prismatic spectrum, from the more to the less refrangible 

 region, be the compression exercised by the prism on the 

 coloured spaces, increasing as the refrangibility is less, 

 we ought not to find any such peculiarity in the diffraction 

 spectrum. In this the coloured spaces are arranged 

 uniformly, and without compression in the order of their 

 wave-lengths. An extinguishing light ought to obliterate 

 them all at the same moment. 



Having modified the common spectroscope by taking 

 away its dark box, so that the slit-tube and the telescope 

 tube could be set in any required angular position to each 

 other, I put in the place of its prism a glass grating, in- 

 clined at 45° to rays coming in through the slit. The ruled 

 side of the grating was presented towards the slit. Now 

 when the extinguishing flame was properly placed before its 

 ground glass, the plane face of the grating reflected its 

 light down the telescope-tube. In this, as in the former 

 case, the spectrum of a small flame before the slit was 

 seen in the midst of a field of light, the intensity of which 

 could be varied by varying the distance of the extin- 

 guishing flame. It was now found that as the brilliancy 

 of the extinguishing illumination increased, all the 

 coloured spaces disappeared at the same moment, and on 

 diminishing the illumination all the colours came into 

 view at the same time. As long as the red was visible 

 the violet could be seen. 



From this it follows that in the diffraction spectrum the 

 luminous intensity is equal in all the visible regions. In 

 the memoirs now publishing I have applied these facts to 

 the case of the spectrum distribution of heat. 



John William Draper 



University of New York 



THE NEW THERMO-ELECTRIC LIGHT 

 BATTERY 



IT appears that a difficulty which it has long been the 

 ambition of practical electricians to overcome has 

 at last been solved by M. Clamond. According to his 

 statement, published in La Lumilrc Electrique, which is 

 confirmed by the Count du Moncel, M. Clamond has suc- 

 ceeded in producing the electric light by means of his 

 new thermo-electric battery. M. Sudrd has also just pub- 

 lished his design for a powerful thermo-electric battery, 

 but we do not know whether this system has yet been put 

 to any practical trial, whereas that of M. Clamond is now 

 in actual use for the purpose of lighting certain factories 

 in Paris. Full details of either system have not yet come 

 to hand, so that it is only possible to state the general re- 

 sults at present obtained. 



That heat could be transformed into electrical energy 

 was first discovered by Seebeck in 1822, who found that 

 an electric current was produced when the junction of two 

 dissimilar metals was heated. Little use, however, was 

 made of this discovery as a source of energy, owing to 

 the feebleness of the current to which it gives rise, al- 

 though it has been of great service since the time of 

 Forbes and Melloni in the investigation of radiant heat. 



