Notices respecting Sen- Boohs. 731 



cases a locus of no current is found running through the centre 

 of the country, and the -f and — currents deduced on either 

 side of this are held to not improbably represent observational 

 uncertainties. 



A special feature is the reduction to sea-level which is actually 

 applied to every observation. Assuming electric currents negligible, 

 the vertical variation of, say, the northerly compouent X is 

 deduced from the observed northerly variation of the vertical 

 component Z by the formula 



JX<h=d7Alv. 



A'ertical variation tables are thus calculated for all the elements 

 and the results are compared with those deduced from formulae of 

 the type cX X= —3h E, where Ris the Earth's radius, and <)X the 

 increment of X with height 7i above sea-level. The latter type of 

 formula follows from the Gaussian potential, neglecting harmonics 

 above the first. The comparison is made for Britain and Austria 

 as well as Japan, and in most cases the accordance is remarkably 

 close: there are differences, however, too systematic to be wholly 

 due to chance. The corrections for reduction to sea-level in the 

 case of the highest stations — fully 34 kilometres above sea-level — 

 are of the order 45y in Horizontal Force and 0'*4 in Inclination ; 

 at most stations they are trifling. 



Considerable mathematical calculation is devoted to an attempt 

 to arrive at the depth and position of magnetic foci to which the 

 observed irregularities in the Hues of magnetic force may be 

 ascribed. For the foci affecting respectively Japan, Austria, and 

 Britain, depths are found of the order 1000, 1300, and 2600 kilo- 

 metres ; but it is admitted that much uncertainty enters into the 

 figures. 



The isogonic and isoclinal lines and lines of equal force are 

 given in charts at the end, smoothed curves on thick paper, 

 and curves showing the local irregularities on thin transparent 

 sheets, through which the smoothed curves are visible. A coloured 

 geological map is added. The volume, which is handsomely 

 printed in English, is a remarkable tribute to the intellectual 

 activity of Japan, and merits the careful consideration of all 

 -ted in Magnetic Surveys. C. Cjliree. 



imentdk Untersuchung von (Uisen. Von Dr. Morris 

 \V. Tr avers, F.Jl.S. Mil einem Vorwort ran .Sir William 

 Ivamsay, K.C'.B. Deutsch von Dr. Tadeusz Estkkichlr. 

 Privatdozent an der K. K. Jagellonischen Universitat in 

 Krakau. Mit 1 Tafel und 144 in den Text eingedruckten 

 Abbildungen. Braunschweig: F. Yi<-weg und Sohn. 1904. 

 Pp. xii+372. 

 Since the appearance of Bunscn*> GtuometrUche Methoden no 

 comprehensive treatise on the subjecl of the experimental inves- 

 tigation of gases was published until Dr. Travers gave an account 

 of recent work in this direction in his well-known book, which 



