NA TURE 



[Janaury 6, 1 910 



is the fact that the magnetic elements are constantly 

 changing. The only satisfactory way of eliminating 

 this trouble is by reference to a recording magnetic 

 station within reasonable distance of the point at 

 which the absolute observations are taken. Unfor- 

 tunately, there is no such station in South Africa, and 

 thus Prof. Beattie has been severely at a disadvantage. 

 He has attempted by other means to eliminate the 

 effects of periodic and secular change, but after giving 

 an account of his attempts he concludes that the result 

 is somewhat illusory, and probably most impartial 

 readers will agree with him. This naturally sets a 

 limit to the general accuracy, and unfortunately it is 

 a case in which the excellent maxim of considering 

 the pennies does not ensure that the pounds will 

 behave with their reputed propriety. 



A statement of the reduced results and tables for 

 the purpose of drawing charts of equal values of any 

 element naturally occupies a considerable proportion 

 of the book. 



The problem of drawing equivalent curves from 

 observations at discrete points calls for great experi- 

 ence and discrimination on the part of the operator. 

 As regards the main features, no question can arise. 

 The results agree well with the known geological 

 formation, of which an excellent map is given. More- 

 over, the localisation of magnetic districts is fairly 

 definite and must prove of value to geological and 

 mining science; but some of the minor fluctuations 

 may as well be due to local magnetic matter as to 

 Incidental error, from which, under the conditions, the 

 observations cannot be quite free. The manner of 

 presentation of the results will, we feel sure, meet 

 with general approval. We trust that the_ author 

 will not accuse us of unduly exceeding the limits of 

 reasonable criticism if we sugges: that the phrasing 

 " with one instrument first, then with the other, and 

 finally with the one again," is not the most elegant 

 way of describing the operation of comparing instru- 

 ments. Further, X, Y, Z, T so naturally represent 

 the northerly, westerly, vertical components and total 

 force that we deprecate the use of Z for total force 

 and T for the northerly component. 



In appendices which really occupy more than half 

 the volume, a statement of the method of reduction 

 and of the station observations is given. That the 

 observations should occupy so large a space is only 

 right, for we trust that future generations will desire 

 to examine the record of this important work. In 

 Appendix D the author gives a typical example of 

 reduction of the determinations of horizontal force. 

 We observe that Prof. Beattie estimates times in the 

 vibration experiment to one-twentieth of a second. 

 While several magneticians adopt this practice, we 

 have some doubt whether, by counting chronometer 

 ticks, one can always be certain of one-tenth of a 

 second. Even with an electric chronograph it is not 

 •customary to estimate a single transit to nearer than 

 one-tenth of a second. 



In the determination of horizontal force a number 

 of points arise. One's object being the value at a 

 definite instant, we require a vibration and deflection 

 experiment. In taking a vibration experiment, both 

 before and after the deflection experiment. Prof. 

 Beattie is well advised, but we are unable to follow 

 the logic of his elaborate system of taking means. 

 If the change in horizontal force during the experi- 

 ments is linear and small, it will not make the least 

 difference whether we take the average of the first 

 and second vibration experiments or adopt _ Prof. 

 Beattie's more elaborate procedure; while if the 

 question enters on squares and non-linear change, we 

 would point out that this has not been examined fully 

 on the theoretical side. Again, we notice that the 

 NO. 2097, VOL. 82] 



practice of reversing the magnet at a given distance 

 was followed. A really better average is got by 

 changing the distance on each reversal of the magnet 

 according to the Kew practice. Whatever the elab- 

 orate way of combining the results may mean, it 

 does not eliminate the frequent possibility of the 

 value of H during the deflection experiment being 

 different from the average value during the two 

 vibration experiments, nor the fact that H may differ 

 for the 30-cm. and the 40-cm. distances in the 

 deflection experiment. These are, however, criticisms 

 of detail, and do not affect the general accuracy of 

 the final result, and the record of the first South 

 .\frican survey will remaiji a memorial to the industry 

 and conscientious work of its director. 



G. W. W. 



M. BOUQUET DE LA GRYE. 

 A MONG French men of science, few have been 

 ■^*- more respected or have worked more inde- 

 fatigably than M. Bouquet de la Grye, whose death, at 

 the advanced age of eighty-two, was recently an- 

 nounced. His official work was more immediately 

 connected with engineering and hydrography, but his 

 scientific interests were wide, and he was equally well 

 known as an astronomer and geodesist. As marking 

 his qualities as a hydrographer, it is sufficient to recall 

 that at an early age, shortly after leaving the Ecole 

 Polytechnique, he took a prominent part in charting 

 the parts of the Mediterranean adjacent to the coasts 

 of Italy and the Island of Elba. To estimate correctlv 

 the importance of this work, we must remember that 

 in the early 'fifties, methods of surveying were not so 

 systematised as they have since become, and 

 mechanical routine had not displaced opportunities 

 for original treatment. Subsequently, he was en- 

 gaged in correcting the charts of the French Atlantic 

 coast, and in the course of this work he assisted in 

 improving the navigation of the River Loire and con- 

 tributed greatly to the establishment of the successful 

 port of Nantes. His work on river navigation, and 

 his appreciation of the facilities for traffic which 

 mland waterways offered, seem to have inspired him 

 with the hope of converting Paris into a seaport, 

 utilising the Seine, which he proposed to deepen for 

 the purpose, and avoiding its irregular bends by the 

 construction of canals. A system of docks and the 

 whole machinery of a seaport were to be constructed 

 at Saint Denis. Needless to say that this project, 

 which demonstrates the extent of the imagination and 

 enterprise of the regretted man of science, has not met 

 with public favour. It seems to be the fate of canals 

 cither to be rendered useless by the increasing growth 

 in the tonnage of steamers, or to involve such gigantic 

 expenditure in construction that their commercial 

 success is jeopardised at the outset. 



In his astronomical work, M. Bouquet de la Grye 

 will be remembered in connection with his loyal and 

 long continued efforts to render the observations of 

 the transit of Venus available for the determination of 

 the solar parallax. In 1874, and again in 1882, he 

 took active part in the preparations and in the actual 

 observations, on the first occasion visiting Campbell 

 Island, and on the second, Mexico. This method of 

 determining the sun's distance may now be dis- 

 credited. Improved technique and greater knowledge 

 have permitted the use of methods of greater accuracy, 

 providing results less difficult of interpretation; but 

 it would be ungenerous to undervalue the devotion of 

 astronomers of a past generation, who have been 

 actuated by a sincere desire to benefit science and 

 have exhibited both ingenuity and energy in the pur- 



