248 



NATURE 



\yan. 12, I 



the Mediterranean littoral. These observations comprised 

 all that was known respecting the distribution of the 

 magnetic elements and rate of secular change in France 

 prior to the appearance of the important work which 

 forms the subject of this notice. 



The observations of M. Moureaux were undertaken 

 at the instigation of M. Mascart, the Director of the 

 Meteorological Observatory of the Pare Saint Maur, and 

 were made during the years 1884 and 1885. A few 

 observations made in 1882 by M. Mascart and M. 

 Moureaux in the neighbourhood of the Pyrenees are also 

 included. A description of the instruments employed, of 



the methods of observation, together with a detailed 

 account of the results obtained from about eighty 

 stations, fairly well distributed over France, constitute 

 the subject-matter of this memoir. 



As the instruments employed by M. Moureaux differ in 

 some important particularsfrom those which are ordinarily 

 employed for field-work by us, it may be desirable to 

 point out their peculiarities. The instruments which are 

 mainly made use of in this country, and which have been 

 employed by English observers who have made magnetic 

 surveys in other parts of the world during the last quarter 

 of a century, are of what is known as the Kew pattern, 



Portable Magnetoir.cter. B, magnet ; E, apparatus 



for steadying magnet ; N, level ; M M', read.ng microscopes ; L, telescope ;\iv, torsion head ; 

 K, bar fjr deflection experiments. 



and embody the results of the experience of such practical 

 magneticians as Lloyd, Sabine, Airy, Welsh, Balfour 

 Stewart, Whipple, and others. Indeed it may be said 

 that almost every observer who has made any extensive 

 series of measurements of terrestrial magnetism has influ- 

 enced the construction of the Kew magnetometer, and 

 there is no question that this instrument, although not 

 absolutely perfect, has now reached a very high degree of 

 excellence. In some respects, however, the magnetometer 

 employed by M. Moureaux possesses advantages over the 

 Kew pattern, and these are especially evident in surveys 

 over rough and difficult country, and where the means of 



transport are limited. In the matter of weight alone there 

 is a considerable difterence. A Kew magnetometer, in 

 its box complete, and exclusive of the deflection bar, 

 which is now usually carried in a hollow leg of the tripod, 

 weighs nearly 50 pounds, whereas that of the French 

 observersweighs only about 9 pounds. A further advantage 

 possessed by the French model is that it is also an alt- 

 azimuth instrument, and hence the observer is less 

 dependent upon the knowledge of true time, afforded by 

 his chronometer, in determining the geographical meridian 

 in a declination observation than he is with the English 

 instrument. In the magnetic survey of Scotland made 



