200 



NATURE 



[June 30, 1892 



not matter, is capable of definition. As Clerk Maxwell tells us 

 that his statements contain all we know of matter and energy, 

 it is clear that these are the only statements by way of definition 

 which he conceives it advisable to give of them, and they are all he 

 does give. I happened to be one of the unfortunate Cambridge 

 students whose first notions of matter and force were obtained 

 from the "Treatise on the Dynamics.ofa Particle," and it was 

 therefore a relief to me when I met with Kirchhoffs 

 '' Mechanik " in 1876, and found the subjectivity of force clearly 

 insisted on. That view of force was in the air of Berlin when I 

 was a student there in 1879. Kirchhoffs services in this matter 

 are referred to with special emphasis on p. 139 of the 

 "Grammar." A perfectly consistent view of force and matter 

 had been published by Mach in 1883. Why the fact 

 that Prof. Tait put forward the "subjectivity of force" 

 in a work of 1885 makes me therefore "a disciple of 

 Prof. Tait," I fail to understand. This statement is the more 

 astonishing, as Prof. Tait directly postulates the "objectivity of 

 matter," but in the same work tells us that " matter is, as it were, 

 the plaything of force." How subjective force can have an ob- 

 jective plaything, perhaps C. G. K. will inform us ; but the 

 statement clearly marks off the standpoint of the "Grammar" 

 from that of Prof. Tait. Mass, according to the "Gram- 

 mar," can only be defined as the ratio of mutual accelerations, 

 and any attempt to connect it with the "quantity of matter" in 

 a body is asserted to be unphilosophical. C. G. K. asks if a pas- 

 sage he quotes from Tait's "Properties of Matter" is not 

 essentially the theory of "ether-squirts"? I reply No, the 

 words "constantly swallows up an amount proportional to 

 its mass," or "at a rate proportional to its mass," sufficing to 

 exclude the mutually enforced flows of ether on which the 

 " Grammarian " bases his applications of ether-squirts to 

 chemical and cohesive actio-is (American Journal 0/ Mathema- 

 tics, vol. xiii., pp. 309-62), Had I ever read, or if read, re- 

 collected. Sir William Thomson's suggestion, it would have been 

 referred to, and a reference to him will be introduced into later 

 editions of the "Grammar." 



C. G. K. very skilfully tries to turn off the "Grammarian's" 

 criticism of the Edinburgh school by representing it as an attack 

 on Newton. The words in the "Grammar" are: "Remem- 

 bering these points we will now turn to the version of the New- 

 tonian laws given by Thomson and Tait " (p. 381). Force, say our 

 writers, is any cause that tends to alter a body's natural state of 

 rest, or of uniform motion in a straight line ; but force, says Prof. 

 Tait, is subjective, and corresponds to nothing which exists outside 

 ourselves. Surely it is a "veritable metaphysical somersault" 

 to then assert that it can be "applied in a straight line"? I 

 fail completely to see how the view that force is subjective is 

 consonant with the definitions and laws put forward by Thom- 

 son and Tait, and asserted by them to be Newtonian. With 

 regard to Newton's own statements, I openly declare that, with 

 all admiration for his genius, I doubt the logical sequence and 

 accuracy of many of his statements with regard to the philo- 

 sophical basis of dynamics. Those who would bind down all 

 time to his views on matter, force, and motion, are much like 

 the geometricians who think it impious to cast out Euclid from 

 school-teaching. Both Euclid and Newton have handed down 

 to us in their pages discoveries which will always form a portion 

 of man's intellectual heritage, but the method in which those 

 discoveries are presented will vary from age to age with in- 

 creasing clearness in man's conceptions of mental and physical 

 processes. 



f^inally, C. G. K. remarks that my conclusions are "mate- 

 rialistic," by which term I suppose he means that he disagrees 

 with them. As one of the chief objects of the "Grammar" 

 is to cast the term matter forth from scientific language, it would 

 have been more correct to say that my conclusions are "ideal- 

 istic." I fear C. G. K. has a more supreme contempt than the 

 majority of the countrymen of Reid and Hume for an accurate 

 use of philosophical language. Karl Pearson. 



Immunity of the African Negro from Yellow Fever. 

 This point, interesting to anthropologists, is raised anew by 

 a writer on the history of epidemics (Nature, June 16), who 

 asks whether the alleged protection is supported by all recent 

 authorities. Recent authorities are not so well placed for judging 

 of this matter as the earlier ; for the reason that immunity is 

 not alleged except for the African negro of pure blood or un- 

 changed racial characters, and that these conditions of the 



NO. I 183, VOL. 46] 



problem have been much less frequently satisfied in the yellow- 

 fever harbours of the western hemisphere since the Africaa 

 slave trade ceased. However, there was a good opportunity in 

 1866, during the disastrous yellow fever anfiong the French 

 troops of the Mexican expedition when they lay at Vera Cruz. 

 Among them was a regiment of Nubians, who had been enlisted 

 for the expedition by permission of the Khedive : that regiment 

 had not a single case of yellow fever all through the epidemic. 

 The African negro regiment brought over from the French 

 colonies of Martinique and Guadeloupe had two or three cases, 

 with, I think, one death. The rest of the troops, including 

 Frenchmen, Arabs from Algeria, native Mexicans and Creoles, 

 had no immunity whatever, but, on the other hand, a most 

 disastrous fatality. The medical officers of the French service 

 have recorded the facts principally inthe Archives de Midecine 

 Navale, their conclusion as to racial immunity being the 

 same that has passed current among the earlier authorities as a 

 truth of high general value (admitting, of course, of exceptions 

 in special circumstances), and a truth that has never, so far as 

 I know, been formally controverted by anyone, although other 

 points concerning yellow fever have been the subject of as 

 obstinate controversy as those touching small-pox itself. The 

 experiences of the French at Goree, a town with ten times as 

 many negroes as whites, exactly confirmed those of Vera Cruz 

 in the same year {Arch, de MM. ttav., ix. 343). 



The immunity of the African negro from yellow fever has 

 become a paragraph in some anthropological text-books, —it-is 

 from the anthropologists, and not from medical authorities, that 

 Darwin cites the fact in his " Descent of Man," adding an 

 original theory of the immunity, which he w as unable to establish 

 after much inquiry. His theory, I need hardly say, was not 

 that " negroes in infancy may have passed through some disease 

 too slight to be recognized as yellow fever, " — whatever that may 

 mean — " but which seems to confer immunity. " The theory, 

 however, is another story, or " another voiume," as the writer 

 just cited is pleased to suggest ; and as for the historical fact of 

 immunity, no one denies it, unless it be Dr. Pye Smith in his 

 recent Lumleian lectures {Lancet, April 23, 1892, p. 901), who 

 gives no reasons. 



It is unfortunate that the anthropologists (Darwin among 

 them) should have introduced one element of dubiety in placing 

 mulattoes on the same footing, in respect of immunity, as 

 negroes of pure descent, and another in mixing up malarial or 

 climatic fevers with yellow fever. C. Creighton. 



June 20. 



The Line Spectra of the Elements. 



I SEE by Prof. Stoney's letter that I have not yet succeeded 

 in making myself understood, as he does not enter on the subject 

 of my objection. A function of the time may well, with any 

 assigned degree of accuracy and for any length of time, be ap- 

 proximately represented by a sum of circular functions, and 

 nevertheless the periods, amplitudes, and phases may not 

 approach definite values when the length of time for which the 

 approximation is to hold good is increased indefinitely. I 

 think this is quite clear from the example I have given in my last 

 letter (p. 100), and it is not necessary to write out other examples. 

 Now, Prof. Stoney shows how one may find by Fourier's 

 theorem the amplitude >, periods, and phases of a sum of circular 

 functions if one only knows the values of the sum. This deduc- 

 tion is not new to me. I worked out the same equations in a 

 slightly different form, when Prof. Stoney's first letter made me 

 further think about the subject. The deduction does also apply 

 to functions that are approximately represented by a sum of 

 circular functions, but only under the restriction that the time 

 for which the approximation holds good is long in comparison 

 to the longest period of the circular functions. In chapter iv. of 

 his paper " On the Cause of Double Lines, &c. " (Transactions of 

 the Royal Dublin Society, 1891), Prof. Stoney should have added 

 this restriction. Then the question would naturally have arisen 

 how the restriction follows from Prof. Stoney's hypothesis on 

 the origin of the line spectra. I do not venture to say that it 

 does not, but the author would have to prove it. 



C, RUNGE. 



Technische Hochschule, Hannover. 



The Nitric Organisms. 

 I MUCH regret to learn from your last issue that Mr. Waring- 

 on considers that I failed to do justice to his work on this 



