458 



NA TURE 



[September 22, 1923 



thousand times the received signal, and higher in 

 special cases. New wireless apparatus, shown by the 

 Marconi International Marine Comtnunication Co., 

 I.tfl., einl>raced direction finders for use in ships, a 

 sj I lid installation for ships' lifelx)ats including direc- 

 ii Ml linding e<iuipnient. and a duplex telephone set — 

 (Itsif^ned to enable ships within 50 miles of land to 

 conununicate by telephony with offices on land, 

 utilising on land the on ii nary telephone installation. 

 The last is at present under trial at Southampton in 

 co-operation with the General Post Office. (3ther 

 very recent apparatus included a small X-ray 

 spectrograph (Ad.un Hilger, Ltd.), made to the design 

 of Dr. A. Miilh I, eml)odying details valuable for the 

 analysis by cr\ st.d structure of crystals and |X)wders, 

 and a barograph of special construction for survey 

 work (by Negretti and Zambra). The latter has a 

 range of 4 inches on the chart to represent i inch 

 variation of barometric ])rcssiir(', ;ui(l the instrument 



can be set to a standard barometer, anywhere from 

 25 in. to 31 in. of mercury, the temperature com- 

 pensation being effective over tliis range. Mr. S. G. 

 lirown's freiK/iiiioiii- was another exhibit on which 

 attention wa a new " loud speaker " 



in which m.i ind is obtaine<l by an 



ingenious meclianit al dev»«.« dependent on the great 

 friction existing Ixjtween cork and glass. 

 But, in the space of a short article, j' 

 be done to all the interesting and instrii 

 contained in the convenient and well - illuiLraicd 

 handbook issued by the exhibition committee. The 

 local officers of the Association, th- ' ' 

 mittee, and, in particular, the 

 committee, Capt. r. VV. Bain, are to \>v Loni;r,uuM'' m 

 on the success of this new departure, and it is to l>c 

 hoped that they may be rewarded by seeing the 

 present exhibition as the first of a long series in future 

 years. M V ( '. i i-.i 1 i t 



Terrestrial Magnetism in France.* 



A DECREE of July 28, 192 1, created an Institute of 

 '^^*- Geophysics attached to the Faculty of Science 

 of the University of Paris, and the new institute has 

 assigned to it the work in terrestrial magnetism 

 previously entrusted to the Meteorological Service. 

 There was established at the same .time a Central 

 Bureau of Terrestrial Magnetism for France and her 

 colonies. The director of both bodies is the editor 

 of the volume under notice, Prof. Ch. Maurain. He 

 contributes an historical account of magnetic observa- 

 tions in France, and a study of disturbances due to 

 electric traction. Recent magnetic history in France, 

 as elsewhere, is mainly a tale of the devastating 

 effects of electric traction. Pare St. Maur, which 

 commenced its career as a magnetic observatory in 

 1883, had to be replaced in 1901 by Val Joyeux, 

 and fears are now entertained for the future of Val 

 Joyeux. There are already two electric lines in the 

 district, one coming within 4400 metres, the other 

 witliin 3000 metres of the observatory. 



A discussion by M. Baldet of observations made 

 at Berizarea in Algeria represents magnetic work done 

 in the colonies. The greater part of the volume, 

 pp. 38-249, is, however, devoted to a discussion by 

 M. Ch. Dufour of the magnetic observations at Val 

 J oy eux from 1 9 1 5 to 1 92 1 . This practically represents 

 seven years' work rolled into one. In the earlier 

 part of the memoir the results of the same species 

 for the seven years appear in immediate succession. 

 Thus we have 9^ consecutive pages of Fourier co- 

 efficients for the diurnal variation of D (declination) 

 and H (horizontal force) calculated for every month 

 from January 1915 to December 1921, while pp. 60-94 

 are devoted to a description of the magnetic dis- 

 turbances recorded during the 84 successive months. 

 The principal magnetic storms are dealt with in 23 

 plates at the end of the volume, Z (vertical force) 

 curves being reproduced as well as D and H. The 

 time scale is only i cm. to the hour, and details of 

 rapid oscillations are difficult to follow, especially for 

 the largest storms, among which the storm of May 

 14-15, 1921, is pre-eminent. A rather unusual 

 feature is that movement up the sheet represents 

 decrease in all three elements. On p. 95 is a r6sum6 

 of mean absolute values of seven elements at Val 

 Joyeux from 1901 to 192 1. The plan of the work 

 then alters, the years being treated separately. The 

 material given for each year has some special features. 



. > Annates de I'lnstitut de Physique du Globe de I'Universitd de Paris et 

 du Bureau Central de Magn^tisme Terrestre. Publiees par les soins de 

 Prof. Ch. Maurain. Tome Premier. (Paris: Les Presses univerytaires 

 de France, 1923.) 



NO. 2812, VOL. 112] 



There are, first, for each month mean <i<iii\ \rtiui.s 

 for D, H, and Z, and hourly values confined to 6h, 

 I2h, i8h. and 24h. The absolute daily maximum 

 and minimum of D and their times of occurrence are 

 included, and a word or two describes the character 

 of the day. Then follow diurnal inequalities for the 

 12 months, apparently from all days, for 7 elements, 

 and a table containing mean values for the 24 hours 

 of the representative day of the year, derived respect- 

 ively from all days and from quiet days. Following 

 this is a most elaborate presentation of results from 

 the five international quiet days of each month. 

 Absolute values are given for each hour of each day 

 for six elements. 



The last part of the volume, pp. 250-298, contains 

 a most valuable discussion of the magnetic results 

 at Pare St. Maur and Val Joyeux from 1883 onwards 

 by the veteran magnetician, M. A. Angot, late 

 director of the Meteorological Bureau. This is a 

 perfect mine of information for the magnetician. 

 We have first diurnal inequalities for D, H, Z, and I 

 (inclination) for the twelve months, derived inde- 

 pendently from 18 years' records at Pare St. Maur, and 

 from 17 years' records at Val Joyeux, stations both in 

 the neighbourhood of Paris. Then we have diurnal 

 inequalities for seven elements based on the whole 

 35 years, and ascribed to Paris. Following this there 

 are Fourier coefficients for the 24-, 12-, 8-, and 6-hour 

 waves corresponding to these inequalities. An ela- 

 borate investigation is made into the possibiUty of 

 representing the annual change in the ampUtude and 

 phase of the several Fourier waves in terms of the 

 longitude of the sun in its apparent annual path. 



Another question minutely considered is the 

 annual variation, meaning thereby the variation left 

 in the mean monthly values of the elements after the 

 elimination of the secular changes, assumed to progress 

 at a uniform rate throughout the year. Use is 

 made of mean monthly values of seven elements 

 from 1883 to 1920, recorded in tables on pp. 278-284. 

 The range obtained for the annual inequality in 

 D. 0-23', seems the smallest found an^nvhere as yet, 

 but a suspicious feature in previous results has been 

 the tendency for the apparent range to dimiiiish as 

 the number of years available has increased. For 

 most of the other elements there are quite substantial 

 ranges, e.g. o-8o' in I (maximum in November, 

 minimum in June), and 17-37 in H (maximum in 

 June, minimum in November). The ranges for these 

 two elements are somewhat larger than those found 

 for Kew * from a shorter period of years, but the 



* Roy. Soc. Phil. Trans., vol, ai6, p. 238, 



