394 



NA TURE 



[February 21, 1901 



LETTERS TO THE EDITOR. 



{ The. Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of rejected 

 manuscripts intended for this or any other part of Natuke. 

 No notice is taken of anonymous communications.'] 



The Size of the Brain in the Insectivore Centetes. 

 I DO not think that there is any recent mammal which has so 

 small a brain in proportion to the size of the skull as has 

 Centetes ecaudatus. In an individual of this species, the pro- 

 perty of the Hon. Walter Rothschild, which was lately living 

 in the Zoological Society's Gardens, I found the total length of 

 the brain to be 28 mm., of which no less than 8 mm. were 

 taken up by the enormous olfactory bulbs. The dried skull of 

 that individual— measured along the base and not taking into 

 account the projecting occipital region — was 96 mm. The 

 greatest diameter of the brain is 16 mm. ; the skull in that 

 region is from 28 to 40 mm. broad. The small size of the 

 brain relatively to the skull has been frequently commented upon 

 and figured in certain of the early genera of Ungulate mammals; 

 and it may be noted that the measurements which characterise 

 Centetes, undoubtedly an early type of mammal, are by no 

 means unlike those of such a genus as Coryphodon, judging, that 

 is to say, by the published figures of the brain cast and skull 

 of that animal. The resemblance is increased by the small 

 size of the cerebral hemispheres, and by the complete exposure 

 of the corpora quadrigemina in Centetes. I hope shortly to 

 give a fuller and illustrated account of the brain of this 

 Insectivore. Frank E. Beddard. 



Thermochemical Relations. 



In a letter in Nature of February 7 (p. 348), Signor Carlo 

 Del I.ungo calls attention to certain thermochemical equalities, 

 and asks for an expression of opinion as to whether these are 

 the result of a casual coincjdence or of a definite law. The 

 equalities in question, if they were not accidental, would have 

 an extremely important bearing on thermochemistry generally, 

 but unfortunately, I believe, they are probably mere accidents 

 of coincidence. 



The two instances given would seem to indicate that when two 

 elements combine together, the heat evolved is equal to the sum 

 of that which is liberated when these same two elements combine 

 separately with some third. Thus we have (modifying Signor 

 Del Lungo's equations so as to indicate more clearly that the 

 heat of combination refers to that of the elements taken in their 

 ordinary molecular condition) : — 



i(2Cl2, O.,) + 4(2H2, O.J = (H,„ CI.,) 

 - 14 Cal. -h 58 Cal. •-= 44 Cal. 

 and 



(2Hj, Csol.) + (Oo, Csol.) = (2H0, O2) 

 19 Cal. + 97 Cal. = 116 Cal. 



I have little doubt but that such coincidences might be shown 

 to be accidental by the existence of similar sets of compound, 

 the heats of formation of which show no such relationship. Un- 

 fortunately, I have with me no thermochemical works to supply 

 the requisite data. An examination of the above instances, 

 however, will, I think, suffice to prove that the coincidences 

 tannot be the result of any definite law. 



When we expand the first of the above equations so as to 

 represent all the stages involved, and the combinations and 

 separations of the atoms in the various molecules, we get : — 



[-(CI, ci)-4(0, o) + (2Ci, o)] 



+ [-(H, H)-i(0, 0) + (2H, 0)] = 

 [-(H, H) - (CI, C1) + 2(H, CI)], 

 which simplifies into 



(CI2, O) -f (2H, O) = (O, O) + 2(H, CI). 



This would mean that any pair of the four groups of atoms in 

 the following diagram would combine together in any way, and 

 yet liberate the same amount of heat — i.e. the thermal result 

 would be the same whether the products were oxygen gas and 

 hydrogen chloride, or water and hypochlorous anhydride. 



O : 2CI 



This, if established as a generality, would be of fundamental 

 importance. But it is inherently improbable, and the existence 

 of the second instance given by Signor Del Lungo seems to' 

 render it untenable. If it were true as regards the gases 

 figuring in the above reaction, it would certainly not be true 

 if one of the products concerned were in the solid condi- 

 tion ; if, for instance, we dealt with solid instead of gaseous 

 oxygen, there would be a divergence from equality equal to the 

 heat of condensation and solidification of oxygen. Yet the 

 second instance given by Signor del Lungo contains terms of 

 this very character. When treated as above, assuming for the 

 sake of simplicity that solid carbon molecules contain only two 

 atoms, it gives 



C ': 2O 



Ci4H 



Thus the two instances given, inasmuch as they are necessarily 

 dissimilar, must by their coincidence show that this coincidence 

 is the result of accident, and not of any thermochemical law. 



Woolacombe, February 12. Spencer Pickering. 



O 2H 



NO. 1634, VOL. 63] 



The Fraunhofer Lines in the Spectrum of the Corona. 



In some of the preliminary reports of the observations made 

 during the last eclipse, undue importance appears to have been 

 attached to the supposed absence of the Fraunhofer lines from 

 the spectrum of the corona. Mr. Newall, for instance {Roy. 

 Soc. Proc, vol. Ixvii. p. 365), says, " it is difficult to reconcile 

 the marked polarisation (of the coronal light) evidenced in this 

 investigation with the absence of Fraunhofer lines in the spec- 

 trum of the corona." Mr. Abbot, whose bolometric observations 

 appear to him to indicate that the corona does not reflect much 

 solar light, states that "additional evidence against the theory of 

 reflecting particles is found in the Indian eclipse spectroscopic 

 results of Campbell, who found a continuous spectrum from the 

 inner corona with total absence of dark lines" {Astrophys. Journ., 

 vol. xii. p. 75). 



Prof. R. W. Wood (Nature, vol. Ixiii. p. 230) has al- 

 ready suggested a partial reconciliation of the apparently con- 1 

 flicting observations, but there are other points which do not \ 

 seem to have received sufficient attention. * 



It must be remembered that the Fraunhofer lines were observed 

 inthe.corona of 1871 by Janssen, and were subsequently photo- 

 graphed by Schuster in 1882, and by Hills in 1893, besides 

 having been seen by various observers on other occasions. Great 

 weight seems to have been attached to the photographs taken in 

 1898 and 1900, in which no dark lines were recorded, but I 

 venture to suggest that the apparent absence of the lines oi> 

 these occasions was mainly due to the use of spectroscopes of 

 too great a dispersion to exhibit them. While great dispersion 

 is well adapted to render the bright line spectrum more effective,, 

 it is clearly fatal to the dark line spectrum, as in the observation 

 of solar prominences. As a matter of fact, the recent photographs 

 only show continuous spectrum extending to a few minutes from 

 the sun's limb, and if one may take the evidence of the prismatic 

 cameras, this arises mainly from the bright line giving inner 

 corona, which probably does not^hine chiefly by reflected light, 

 and would, therefore, not necessarily show the Fraunhofer lines. 

 This view accords well with Schuster's account of the photo- 

 graph of 1882, in which it is stated that nearG there was a sharp- 

 decrease in intensity at 0*29 of the solar radius from the linib, 

 a further falling off in intensity at o-6o, with the spectrum fading 

 out of view at i "47 ; in the lower regions the spectrum was per- 

 fectly continuous, but in the upper regions the solar line G was 

 reversed. Captain Hills also found, in 1893, the Fraunhofer 

 lines only at a considerable distance from the limb. Stone, too, 

 in 1874, observed the dark lines in the outer, but not in the 

 inner corona. In these early observations and photographs we 

 may take it that the dispersion of the spectroscopes employed 

 was much less than in 1898 and 1900, and it would therefore 

 seem desirable to search for the Fraunhofer lines in the next 

 eclipse with instruments of smaller dispersion than those recently 

 in use for the bright line spectrum and special observations. 



It may be further remarked that as we do not see a section 

 of the sun, the outer corona must be superposed upon the inner,, 

 and the fact that the Fraunhofer lines have not been observed 

 or photographed in the inner corona, even with small dispersion, 

 is sufficiently explained by the superposition of the dark line 

 spectrum on the much stronger continuous spectrum of the inner 

 corona. Such superposition would, of course, be more effective 



