December i, [898J 



NA TURE 



LETTERS TO THE ED 11 OR. 

 [The Editor does not hold himself responsible for opinions ex- 

 prcssei by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 minitscrifts intended for this or any other part of NATURE. 

 Xo notice is taken of anonymous commiiniiations.'\ 



Asymmetry and Vitalism. 



That portion of Prof. Karl Pearson's letter in Nature of 

 Nov. 10 which deals with chemical problems is largely based 

 on misconceptions of the meaning of terms used by chemists. 

 Thus, after quoting a statement of mine regarding optically 

 active compounds, he says: "An optically active compound 

 means merely a preponderance of one kind of enantiomorph." 

 That is precisely what it does not mean ; that would be an 

 optically active niixture. No chemist ever uses the word 

 "compound" when he means "mixture"; I meant one kind of 

 enantiomorph and one only. Moreover, I explained this point 

 in detail in my first reply. Prof. Percy Frankland, as a 

 chemist, has of course found no difficulty in following my 

 meaning ; he says that the question which I raised was : " the 

 possibility of producing, without the interference of a living 

 agency, an optically active substance unaccompanied by its 

 fiiantiomorph.'^ A great part of Prof. Pearson's letter is there- 

 fore devoted to combating an opinion which I never expressed, 

 and I am consequently relieved from the necessity of further 

 discussing this part, or of calling attention to similar mis- 

 conceptions which it contains. One point, however, I must 

 notice. Prof. Pearson complains that I have supposed that he 

 meant "twenty" molecules and no more, when in reality he 

 referred to twenty tosses of a coin ; and he adds that he was 

 willing to assume the formation of a million molecules. I was 

 led to take his words in the former sense by my impression — as 

 it now appears, a mistaken impression — that he really under- 

 stood that I was arguing about single asymmetric compounds; 

 and I imagined that he purposely assumed the formation of only 

 a small number of molecules in order that they might conceiv- 

 ably be all of one kind of asymmetry. 



The part of the letter which I wish especially to consider is 

 that in which Prof. Pearson suggests a hypothetical symmetric 

 mechanism by which he believes a separation of enantiomorphs 

 might be effected. This suggestion, if valid, strikes at the root 

 of a generally accepted principle of molecular asymmetry. I 

 can sincerely say that it is with the utmost diffidence that I 

 venture to call in question any result that Prof. Pearson has 

 arrived at by a mathematical process. But in the present case, 

 I have tried in vain to follow his reasoning ; whilst, if I work 

 out the problem in my own way, I arrive at a conclusion exactly 

 the opposite of his. I have no choice, therefore, but to state 

 my results, and to ask Prof. Pearson to correct me if I am 

 wrong. 



The tetrahedral representation of two enantiomorphous mole- 

 cules, each containing a single asymmetric carbon atom, is given 

 in my address (Nature, vol. Iviii. p. 455). The tetrahedra 

 (figs. I and 2) are assumed to be irregular; the four different 

 atoms or groups are situated at different distances from the 

 central carbon atom to which they are attached ; the two tetra- 

 hedra are enantiomorphous. It must be carefully borne in 

 mind that in these two structures all corresponding molecular 

 dimensions are identical ; the two structures differ only in their 

 opposite asymmetry. 



Prof. Pearson imagines a thin cylindrical sheet of optically 

 inactive mixture to be whirled round the axis of the sheet ; and 

 he argues that owing to the position of the centroid in these 

 enantiomorphous tetrahedra, the one kind might be in sta/tlc 

 equilibrium when, say, their -\' angle .sets inwards, and the other, 

 when this sets outwards ; " or at least some similar like differ- 

 ence of positions will differentiate like from unlike enantio- 

 morphs." Then, on allowing a strip of the cylindrical surface 

 placed horizontally to fall through a viscous fluid, the difference 

 of resistance caused by this difference of position may effect a 

 separalion of the two kinds. 



As I have said, I am unable to follow this reasoning. I 

 should discuss the problem as follows : 



Let H, .\', y', z' (Figs, i and 2, loc. cil.) represent the four 

 different atoms or groups attached to the central carbon atom ; 

 and, as regards their masses, let H<x', x'<y', and Y'<z'. 



Then, supposing a thin cylindrical sheet of substance consi.st- 

 ing of equal numbers of the two enantiomorphous tetrahedral 



NO. 15 18, VOL. 59] 



forms to be whirled about its axis, each tetrahedron, whether 

 right-handed or left-handed, will be in stable equilibrium when 

 the distances of the foregoing groups from the axis of rotation 

 of the sheet are in the order H, x', v', z'. Therefore the edge 

 y' z' of either tetrahedron will be nearer to the outer surface of 

 the sheet than the edge H x'; and each of these edges will be in- 

 clined towards this outer surface so that the ends z' and x', of these 

 edges, are respectively nearer to it than the ends y' and H ; and 

 the inclination of corresponding edges will be the same in both 

 tetrahedra. A linejoining the centroid of the face H x' y' with '/.', 

 and produced through z' to meet the outersurfaceofthe sheet, will 

 form the same angle with this surface, whether the tetrahedron 

 be right-handed or left-handed. Right-handed and left-handed 

 molecules will therefore be affected in exactly the same manner 

 when a strip of the cylindrical surface is placed horizontally and 

 allowed to fall through a viscous fluid ; and no separation of 

 the two kinds will occur. The "difference of positions" 

 which Prof. Pearson demands, does not extend beyond the fact 

 that a continuous curve passing towards the surface of the sheet 

 through the groups H, x', y', z' in succession, will in the one 

 set of tetrahedra describe a right-handed, in the other a left- 

 handed helix. 



I am unable to arrive at any other conclusion than the fore- 

 going. 



Prof. Percy Frankland's suggestion of a mechanism by which, 

 starting with a single asymmetric molecule, an optically active 

 compound might be produced unaccompanied by its enantio- 

 morph, practically coincides with thit published a little later by 

 Mr. Strong. Such an action is, as I admitted in noticing Mr. 

 Strong's communication, certainly conceivable, although, as an 

 .actual process occurring under chance conditions, it is exceed- 

 ingly improbable. I regret that I overlooked the possibility of 

 such an action. 



Prof. Frankland's other suggestion is that, prior to the ex- 

 istence of life on the earth, "t ne asymmetry of solar radiation 

 may originally have determined the exclusive synthesis of one 

 enantiomorph." I had already considered this possibility. It 

 seems to me that the earth's rotation, to which this asymmetry 

 of solar radiation is due, is so slow as compared with the 

 atomic and molecular motions involved in the production of 

 chemical compounds, that it is difficult to understand how it 

 could perceptibly impress its asymmetry on chemical action. 



Although, in view of the arguments adduced by Prof. Percy 

 Frankland and Mr. Strong, I no longer venture to speak of the 

 inconceivability of any mechanical explanation of the production 

 of single optically active compounds asymmetric always in the 

 same sense, I am as convinced as ever of the enormous improb- 

 ability of any such production under chance conditions. The 

 processes suggested by Prof. Frankland and Mr. Strong are 

 purely hypothetical and ace likely to remain so. 



The University, .Aberdeen, November 17. F. R. J.api'. 



Early History of the Great Red Spot on Jupiter. 



Havinc, collected a number of observations and drawings of 

 objects bearing a suggestive resemblance to this feature, and 

 made during the period from September 5, 1831, to November 

 14, 1869, I have been enabled to determine the rotation period 

 during that time. This, t.aken in comhinaiion with my dis- 

 cussion of the observations from November 14, 1869, to July 

 30, 1898 (Nature, August 4, 189S, and Monthly Notices 

 R.A.S., vol. Iviii. No. 9), extends the whole interval over 

 which the spot can be pretty certainly identified to nearly 67 

 years, or 24,435 days, during which the mean rate of rotation 

 was 



9h. 55m. 36'2s. 



and the total number of rotations 



59,071. 



My investigation, though quite satisfactory so far as it goes, 

 would be rendered more certain if further observations or 

 drawings could be secured for the period prior to 1869. I 

 should be much obliged, therefore, if any of your readers having 

 such materials in their possession would supply copies, or allow 

 me to have temporary use of the originals. The red spot has 

 varied its appearance so much that it may either appear as a 

 red oval mark, as an elliptic ring, or be practically invisible as 

 at present, though its place may be clearly indicated by a marked 

 hollow in the southern side of the south equatorial belt. Old 



