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THURSDAY, SEPTEMBER 9, 1909. 



.4 MONOGRAPH ON THE TRANSIT CIRCLE. 

 Les Observations meridienncs : Theorie ct Pratique. 

 By F. Boquet. Tome Premier, Instruments et 

 M^thodes d'Observation. Pp. xi + 314. Tome 

 Second, Corrections instrumentales et Equations 

 Personelles. Pp. iv + 342 + xii. (Paris: Octave 

 Doin et Fils, 1909.) Price, 2 vols., 10 francs. 



THESE two volumes comprise one of two com- 

 pleted sections out of a total of twenty-nine 

 •devoted to astronomy and celestial physics in a new- 

 form of scientific encyclopsedia in which astronomy 

 is only one of forty divisions. The whole work, if 

 and when completed, should run to at least a thousand 

 handy little volumes at a uniform price of 5 francs per 

 volume. An index to the complete series is also 

 promised, but it is hardly contemplated that the 

 demand for the whole set will be very great, the 

 idea being that each subject is to be totally distinct, 

 so that a minimum of irrelevant matter need be 

 purchased by any interested specialist, and that such 

 sections as are rapidly rendered out-of-date may be 

 quickly replaced by revised editions without necessi- 

 tating alteration of the whole work. 



Our purpose now, however, is to deal only with the 

 two volumes before us, premising that the " Biblio- 

 theque d'Astronomie et de Physique celeste," to which 

 they belong, is under the directorship of M. Jean 

 Mascart. It may be fairly remarked, inasmuch as 

 the titles of the other twenty-eight sections of this 

 " Library " are given, that it is quite possible the 

 number will have to be augmented, as there is at 

 present no obvious place for more than one modern 

 investigation without straining the meaning of some 

 of the published titles. With some 600 pages entirely 

 devoted to meridian observations, we are at first in- 

 clined to wonder why so much space was thought 

 necessary. But the wonder does not last long, for 

 the pages are quite small, and the amount of detail 

 is very great, as is only fitting in an encyclopaedia. 

 Moreover, we soon perceive that the transit-circle, 

 though the two parts are inevitably studied separately, 

 is the only instrument considered. This strikes us as 

 an error of omission, for there is no other place for 

 discussion of the zenith telescope in any form. There 

 is no mention of the various forms suggested in sub- 

 stitution for the ordinary one, such as the fixed tele- 

 scope with meridian mirror or the transit with axis 

 view, simply rotating in bearings east and west. A 

 very possible explanation is that these various forms 

 are not of much account in France, but their omission 

 seems to be a mistake. 



There does not seem to be much, if anything, of 

 consequence omitted in reference to the transit circle 

 itself, all kinds of instrumental errors being fully and 

 carefully dealt with, several methods of determina- 

 tion or correction being given in many cases. For 

 instance, a very clear account is given of Cowell's 

 refraction tables as used at Greenwich, while division 

 error and eccentricity, screw value and error, pivot 

 error, wire intervals and inclination, flexure, and so 

 NO. 2080, VOL. 81] 



on, are treated with great fulness. The printing 

 chronograph in various forms is naturally conspicu- 

 ous, this Subject being one on which M. Boquet has 

 written more than once before. Another subject with 

 which he has similarly shown familiarity is given an 

 importance we do not remember to have seen before, 

 and that is personal equation, the adequate treat- 

 ment of which is especially welcome. The various 

 physiological or psychophysiological causes of error 

 are very carefully differentiated, and at the same time 

 no space is wasted on the numerous devices for deter- 

 mining absolute personal equation in transit observa- 

 tions, though a long list of references is given for 

 the use of those who care to pursue the subject. 



Perhaps those whose " eye-and-ear " observations 

 are consciously or unconsciously taken by what may 

 be called the chronometer comparison method, as 

 distinct from Bradley's (M. Boquet calls it " m<5thode 

 de I'oeil et de I'oreille par estime du temps "), will 

 question whether their observations are so inferior as 

 M. Boquet assumes. The use of screens also for 

 magnitude equation is liable to meet with similar 

 objections to those urged against the pierced cube 

 of the Greenwich transit-circle, but in this the author 

 is only summarising what has been done and pro- 

 jected. There are, in fact, very few places where he 

 has expressed a decided personal opinion, so that we 

 are inclined to regret that the plan of the work 

 allowed so little scope for personality. With the reser- 

 vation as to omissions to which we have alluded, 

 we can only hope that the rest of the thousand-odd 

 volumes will maintain the high standard of thorough- 

 ness set by M. Boquet. W. W. B. 



THE HISTORY OF MECHANICS. 

 Lectures de Mecanique. By E. Jouguet. Premiere 

 Partie : La Naissance de la Mecanique. Deuxifeme 

 Partie : L'Organisation de la Mecanique. Pp. x-(- 

 210 and 284. (Paris: Gauthier-Villars, 1908-9.) 

 Price 7.50 and 10 francs. 



SINCE the eventful appearance of Mach's works on 

 mechanics and heat, much greater interest has 

 been shown in the historical development of applied 

 mathematics, both for its own sake and from a grow- 

 ing conviction that the teacher of a subject ought to 

 know something of its actual growth and expansion, 

 as well as the current methods of expounding it. 

 Recent works by M. Duhem show that even in 

 France, the birthplace and home of clear-cut analyti- 

 cal systems, there is an appreciation of the value of 

 historical research and of tracing the slow formation 

 of the leading ideas and principles of mechanics. 



For several reasons M. Jouguet's book will be found 

 a useful supplement to its predecessors. In the first 

 place he is an engineer, so that he is in full sympathy 

 with such men as Stevinus and Huygens and Galileo, 

 and gives considerable attention to those who, like 

 Reich and Andrade, propose to deduce the laws of 

 mechanics from actual experiment. At the same time 

 he is by no means the case-hardened empiric who 

 ignores the claims of logic, and despises speculation. 

 In fact, it is noteworthy, and gratifying, that he prac- 



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