32 



NATURE 



[March 9, 1916 



first part consists of 200 pages, comprising the 

 families Ranunculaceae to Aquifoliaceae, but, un- 

 fortunately, we have to wait for the concluding 

 part of the work for the appearance of the intro- 

 duction and key to the families. Without these 

 the " Flora " loses some of its value and much of 

 its interest, and it is to be hoped that the publica- 

 tion of the succeeding parts will take place as 

 rapidly as may be possible. 



The plan followed in the " Flora " is that 

 adopted by Prain in his "Bengal Plants," and is a 

 plan admirably suited for a local flora where the 

 easy identification of the plant is the object in 

 view. Descriptions of species are therefore 

 omitted, and the whole flora is in the form of key. 

 A description of the natural family is succeeded 

 by a key to its genera. Each genus is concisely 

 described, and a key to its species follows, and 

 then under each species there is no further descrip- 

 tive matter, but only geographical and economic 

 information and vernacular names. In those 

 genera represented by only a single species, a 

 short description is given. The keys are well 

 drawn up, and a good test of their efficacy is to 

 be seen in the genus Impatiens with its seventy 

 species, which are all clearly diff"erentiated. It 

 should be mentioned that Mr. Gamble was assisted 

 by Mr. S. T. Dunn in the preparation of about 

 the first 132 pages of this part. 



The Theory of Abstract Ethics. By T. Whittaker. 

 Pp. viii + 126. (Cambridge: At the University 

 Press, 191 6.) Price 45. 6d. neti' 



This book is the result of stimulus applied, as 

 the author informs us, by Prof. Juvalta's "Old 

 and New Problem of Morality." Though 

 awakened from dogmatic slumber by Renouvier, 

 Mr. Whittaker had continued, in accordance with 

 English tradition, to try to derive the ethical law 

 of justice from "ends" or "goods." But the a 

 priori cannot be avoided ; and if a metaphysical 

 doctrine emerges that is more in harmony with the 

 moral aspirations of mankind, we must not refuse 

 to consider it out of a forced austerity. 



The fundamentals of every moral system are 

 liberty and justice; and abstract ethics, as dis- 

 tinguished from the art of life in general, is a 

 kind of impersonal science of the conditions under 

 which all the types are bound to live in common. 

 In the present state of affairs, however, the 

 author naturally expatiates into concrete ethics 

 and politics, giving a useful summary of Kant's 

 view. The moral law recognised within states 

 should be extended to their mutual relations, with 

 the aim of eternal peace, which will be possible 

 when we have progressed to a permanently 

 superior political society. But he did not postu- 

 late a world-state so much as a family of states 

 each respecting each other's individuality. Fin- 

 ally, on the last page, the author permits himself 

 a legitimate speculation, perhaps too friendly, in 

 the direction of reincarnation, which is certainly 

 one feasible way of resolving many moral prob- 

 lems. 



NO. 2419, VOL. 97] 



LETTERS TO THE EDITOR. 



[The Editor does not hohl himself responsible for 

 opinions expressed by hi^ correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Naturk. No notice is 

 taketi of anonymous communications.] 



The Method of Curves. 



The expression of the results of observations and 

 experiments by curves became common during the 

 first half of the nineteenth century. One of the first 

 instances was given by Perkins {Phil. Trans., 1826) in 

 a paper on the compressibility of water. 



Six years later Sir John Herschel (Trans. Ast. Soc, 

 v., i) gave an account of the method of graphical 

 construction on squared paper as applicable to astro- 

 nomical computations and physico-mathematical in- 

 quiries. 



"The dates in years and decimals are measured as 

 abscissae, and the angles in degrees and decimals as 

 ordinates. The next step is to draw by the mere judg- 

 ment of the eye, and with a free but careful hand, not 

 through but among the points, a curve presenting as 

 few and slight departures from them as possible, con- 

 sistently with the character of large and graceful 

 sinuosity, which must be maintained at all hazards. 



■'But since an equal trustworthiness can probably not 

 be placed on all the observations, we must take care 

 to distinguish those points which correspond to ob- 

 servations entitled to the greatest confidence, such as 

 those which appear to have been made under pecu- 

 liarly favourable circumstances, or which rest upon 

 the average of a very great number of individual 

 measurements. These should be marked on the chart 

 in some special manner not liable to be mistaken, and 

 when we draw the curve we must take care to make 

 it pass either through or very near all those points 

 which are thus distinguished ; or at least to deviate 

 from them with much more reluctance than from 

 such as have no claim to our peculiar attention. 



" By substituting the curve for the points we have 

 made a nearer approach to nature, and in a great 

 measure eliminated errors of observation." 



A few years later Regnault (Mem. Acad. Sci., 1847, 

 xxi., p. 316) reduced the method to a fine art. To re- 

 present the expansion of mercury he used four copper 

 sheets, 80 cm. square, each divided into 10,000 squares. 

 Within these squares values were marked by a special 

 dividing engine, one bevelled edge of the heavy base of 

 which was graduated into 8 mm. divisions and tenths. 

 A carriage running on a half-millimetre screw, the 

 large head of which was divided into 50, so that 

 001 mm. could be accurately measured, carried the 

 burin. Experimental values were marked by the inter- 

 sections of lines drawn by the burin. A free curve 

 was drawn by Regnault, which was completed and 

 engraved by an artist. Even with these precautions 

 a constant error was detected in the last plate. 



The introduction of the copper plate and dividing 

 engine seems to conduce to the accuracy and perman- 

 ence of the record. 



The method has been rendered more easy of appli- 

 cation and possibly more accurate by the introduction 

 of mechanically ruled paper, a good sample of which 

 of French manufacture consists of sheets a metre 

 square, ruled into millimetre squares, each edge of 

 which is divided into 02 mm. by dots. Free hand- 

 curves have also been more or less replaced by 

 mechanically cut curves and flexible laths. 



Notwithstanding- the very general use of the method 

 and many theoretical accounts of it (Whewell, " Nov. 

 Org. Ren.," 1858, p. 204; Stanley Jevons, "Principles 



