50 



NATURE 



^[May 17, 1900 



(including autogamy, endogamy, homogamy, preferential 

 mating or '* sexual selection " in Darwin's sense, and 

 heterogamy) ; and on " genetic selection " or the in- 

 heritance of fertility. The last-named principle promises 

 to be of special weight as a factor in evolution, though 

 the proof of definite correlation of other physical charac- 

 ters with that of fertility must still be considered in- 

 complete. The analysis of natural selection into auto- 

 generic, heterogeneric and inorganic selection (" intra- 

 selection " being ignored) is useful, and might have been 

 carried still further. 



A contribution to the theory of evolution so original 

 and stimulating as Prof. Pearson's must necessarily run 

 the gauntlet of much adverse criticism. This will 

 probably take the form rather of objection to certain 

 points of detail than to the general drift of his method. 

 Certainly some passages and expressions seem capable 

 of amendment. It is, for instance, scarcely allowable to 

 speak of the approach of the coefficient of correlation to 

 unity as " the transition of correlation into causation." As 

 the author himself elsewhere points out, correlation does 

 not imply causation, though the converse is no doubt true 

 enough. The principle of recognition-marks in their 

 widest sense seems again to deserve more consideration 

 than it receives at his hands. They are requisite to 

 ensure the actual effectiveness of the impulse towards 

 preferential mating. It is worth notice in this con- 

 nection that the author's view as to the species-forming 

 tendency of differential fertility (which is distinct from 

 " physiological selection," as understood by Romanes) is 

 well exemplified by Dr. Jordan's work on " mechanical 

 selection." In speaking of hybridisation with reference 

 to atavism, the " Grammar " does less than justice 

 to observed facts. The evidence afforded by crosses, 

 such as those so carefully investigated by Standfuss 

 at Zurich and by Prof. Cossar Ewart at Penicuik, 

 has a bearing on heredity and atavism which cannot 

 safely be ignored. Prof. Pearson contents himself with 

 saying that in such cases, "from physiological and 

 mechanical reasons, the gametes produce a zygote which 

 does not give an individual blending the ancestry. 

 Here any singularity almost may be expected." This 

 statement, to say the least, seems wanting in precision. 

 Again, a severe critic might allege that the author is apt 

 to assume theoretical values (as in the case of the re- 

 semblance of first cousins) which have not stood the test 

 of rigid proof. 



We have not yet learned to like the new term "apole- 

 gamy," nor such a phrase as " a comparative few zygotes " 

 (P- 453)- The remarkable form of a sentence on p. 461 

 is probably due to a printer's error, as also the substitu- 

 tion o# DAG for FAG at the bottom of p. 447. These, 

 however, are small matters, and do not detract from the 

 value of the book. 



We must not be led into a discussion of the earlier 

 chapters, a notice of which appeared in these columns at 

 the time of their original publication. There is, however, 

 one point on which we cannot refrain from joining issue. 

 Prof. Pearson takes biologists to task for the loose way 

 in which they often use such terms as " matter," " force " 

 and " motion," as if no important questions lay behind 

 them. Now it is certain that, in their employment of 

 these expressions, biologists have no desire whatever to 

 NO. 1594, VOL. 62] 



prejudice any philosophical problems. When meta- 

 physicians and physicists are agreed about the definition 

 of these terms, the biologist will doubtless be quite ready 

 to follow suit. Meanwhile he must be allowed the use 

 of ordinary language. But Prof. Pearson maintains that 

 if these words are used in their everyday, or, as he calls 

 it, their " figurative " sense, they ought to be defined. 

 Why so ? No definition is required for the particular 

 end in view. Supposing an opponent were to say that 

 the " matter " of the argument was not " attractive," and 

 that there was no " force " in this or that contention, 

 would the Professor waste time in making him define hi& 

 terms ? C^n we not " beat about the bush " without 

 entering into explanations that would satisfy the school- 

 master and the botanist ? It would seem that here the 

 Professor once more overshoots his mark. 



It will be convenient to give, in conclusion, a summary 

 of the main contention of these new chapters in the 

 author's own words, as follows : — 



" It is not absence of explanations, but rather of the 

 quantitative testing of explanations, which hinders the 

 development of the Darwinian theory." " The problem 

 of the near future is not whether Darwinism is a reality, 

 but what is quantitatively the rate at which it is working 

 and has worked." 



It is noteworthy to find him adding : — 



" If that problem should be answered in a way that is 

 not in accordance with the age of the earth, as fixed by 

 certain physicists, it by no means follows that it is biology 

 which will have to retrace its steps. When the rate is 

 determined, it will be as exact in its nature as physical 

 appreciations ; and it will be a question of superior logic, 

 and not of the superiority of the 'exact' over the ' de- 

 scriptive' sciences which will have to settle any disagree- 

 ment of biology and physics." ..." It is a question of 

 the rate of effective change, and when the biologists are 

 in a position to make a definite draft on the bank of time, 

 their credit will be just as substantial as that of the 

 so-called exact sciences." 



These last sentences, as coming from a mathematician, 

 are highly significant ; and we cannot but admire the 

 courage that has given them expression. F. A. D. 



HERTZ'S MECHANICS. 

 The Principles of Mechanics presented in a Nciu Forin. 

 By Heinrich Hertz. Authorised English Translation, 

 by D. E. Jones and J. T. Walley. Pp. xxviii -I- 276. 

 (London : Macmillan and Co., Ltd., 1899.) 



GREAT expectations were aroused by the publication, 

 in 1894, of a book by Heinrich Hertz, with the 

 title, "Die Principien der Mechanik in neuem Zusam- 

 menhange dargestellt." Perhaps it would set out the 

 received theory of dynamics in strictly logical sequence ; 

 perhaps it would present a complete theory of energy in- 

 dependent of the notion of force ; perhaps it would 

 bridge the gap between the molecular and mechanical 

 standpoints. Whether it would do any of these things or 

 not, what Hertz might have to say would certainly be 

 worthy of attention. Hertz died before the work was 

 printed, and the task of seeing it through the Press was 

 entrusted to Dr. P. Lenard. He tells us that the author 

 had devoted the last three years of his life to the book, 

 the last two being spent in perfecting its form ; and, al- 

 though there are indications that he was not even theri 



