July 14, 1904] 



NA TURE 



24; 



skill ; the orig"inal sentences have to be individually 

 || annihilated before endurable English equivalents can 



be raised from their ashes. This Dr. Ewart has done 

 ^o well that the book reads as though it had been 

 written in English. 



No one can nowadays write a physiological text- 

 book without being largely indebted to Pfeffer's 

 " Pflanzenphysiologie," and this, in his preface, Prof. 

 Jost acknowledges in the fullest way ; but his book is 

 so different from Pfeffer's in scope and manner of 

 presentment that it is essentially an original work. 



It is an eminently readable and useful book; it is 

 written in a clear and easy style, and steers a skilful 

 course between some of the difficulties that beset the 

 lecturer. On the one hand the author avoids placing 

 too much stress on what is new, while he by no means 

 neglects the recent literature, and is thoroughly up-to- 

 date in his treatment of the subject. He is not afraid 

 of facing a difficultv or of pointing out where our 

 knowledge fails to solve the problem. He has pro- 

 duced a book admirably suited to the advanced 

 student of an English university, and one that may 

 also be read with advantage by more advanced workers. 

 Jost's manner of stating his case is so suggestive, and 

 he is so open in pointing to possible lines of inquiry, 

 that the book cannot fail to be useful to a wide class 

 of readers. 



It is divided into three parts: — (i) Stoffwechsel, 

 (2) Formwechsel, (3) Energiewechsel. Part i. deals 

 with the absorption, transport, and loss of water, with 

 the assimilation of carbon and nitrogen, and with 

 respiration and fermentation. Under Formwechsel 

 (part ii.) we have a general statement of the funda- 

 mental problems of development, then come growth 

 and development under constant conditions. This is 

 followed by the effects of the environment on growth, 

 &c., and finally conies a section on periodicity, inherit- 

 ance, and variation. Part iii. (Energiewechsel) deals 

 with hygroscopic movements, growth-curvatures 

 (" tropisms "), the movements of tendrils, of sleeping 

 plants, &c. , and chemotaxis, &c. The whole of part iii. 

 seems to us particularly good, and contains much that 

 is interesting and valuable in the way of discussion. 

 We confidently recommend Prof. Jost's lectures, but 

 I since it is the duty of the reviewer to find some fault, 



we may direct attention to Fig. 141, which is printed 

 upside down. F. D. 



CHRONOLOGICAL CALCULATIONS. 

 Astronomical and Historical Chronology in the Battle 

 of the Centuries. By William Leighton Jordan, 

 F.R.G.S., F.S.S., &c. Pp. 70. (London: Long- 

 mans and Co., 1904.) Price 2S. net. 

 THE main object of this little work is to contend 

 that what is sometimes called the " astronomical " 

 method of dating events prior to the Christian era is 

 really what was intended to be used when the system 

 of using dates before and after the birth of Christ was 

 first introduced. Hence it is dedicated to the librarians 

 of the cities of Florence and Pisa, in the hope of re- 

 ceiving from some of them " further evidence for the 

 elucidation of the subject." 

 NO. t8i I, VOL 70] 



Now divisions of this kind involve the drawback of 

 necessitating a reckoning in two directions. This is 

 also the case, for instance, in the centigrade division 

 of the thermometric scale, which is nearly always 

 avoided by the general public in this country, and would 

 be still more in countries which are nearer the equator, 

 by using Fahrenheit's scale, the zero being below the 

 lowest point usually reached in winter, so that 

 a statement of the reading is sufficient, without 

 adding above or below freezing, as the case may be. 

 In dating an event, too, by Christian chronology, we 

 have to state whether it occurred before or after the 

 birth of Christ (or the year accepted as such), which 

 is indicated by affixing the letters B.C. or a.d. But 

 there is this further complication, as compared with a 

 thermometric or other scale, that a degree is a definite- 

 point, and everybody knows that 1° below freezing is 

 two degrees below 1° above it. A year is not a definite 

 point of time, and we all know (having had a recent 

 instance of it) what perplexity is caused in many 

 minds when a new century has commenced with re- 

 gard to which is the first year thereof. Our author 

 reminds us, for instance, how the German Emperor 

 insisted that the present (twentieth) century began at 

 the beginning of the year 1900. A further complication 

 is contained in the fact that we do not know exactly 

 the date of Christ's birth. 



But although that question is very interesting from 

 an historical point of view, it is too late now to treat 

 of it as a matter affecting our system of chronology. 

 This is based on the assumed fact that the traditional 

 date of the birth of Christ is the end of the year B.C. i, 

 so that one year after it was completed at the end of 

 .A.D. I, a century at the end of a.d. 100, nineteen 

 centuries at the end of a.d. 1900, and the twentieth 

 century commenced on January i, a.d. 1901. 



Some people not versed in chronological calcula- 

 tions fancy that astronomers go out of their way toi 

 differ from ordinary people when they call the year 

 which is commonly reckoned B.C. i (the year preceding- 

 A.D. i) o, and denominate B.C. 2 as the year — i. But 

 there is no such affectation of singularity in the matter;, 

 a necessity is laid upon the computer in this respect,, 

 for if we subtract 1 from i, the result cannot be any~ 

 thing but o, and if we subtract 2 from i, the result 

 must be —I. It is necessary, therefore, to remind 

 ordinary people that if they desire to estimate the 

 number of years from a date in B.C. reckoning to one- 

 at the same season in a.d. reckoning, it is not sufficient 

 to add the years together, but unity must be sub- 

 tracted from the result; from June i, B.C. 10, for 

 instance, to June i, a.d. 10, is an interval of not 

 twenty, but only nineteen years. 



The author of the work before us desires to prove 

 that those who first used Christian chronology in- 

 tended that it should be reckoned in this way, the 

 numbers being not cardinal, but ordinal. However, 

 that is a mere matter of curiosity. An inmate of a 

 lunatic asylum, who appeared sane to a visitor, was 

 once asked why he was there. " Oh," he said, " I 

 thought everybody else was mad, and they thought I 

 was ; as they were in the majority, they had their way 

 with me, and so I am here." 



