abstracts: terrestrial magnetism 179 



longitude 25° 52', the average annual change is -10'.9; for the region 

 of the mean south latitude 35° 16' and east longitude 74° 46' the mean 

 average annual change is +13'.2; and for the region of the mean south 

 latitude 25° 17' and east longitude 60° 35' the average annual change is 

 +5'.4. The mean secular changes corresponding, as taken from the 

 British Admiralty chart and the United States Hydrographic Office chad 

 above referred to, are respectively - 2'.5, +2'.5, - 2'.2. The plus Bign al - 

 tached to the secular change indicates that west declination is at presenl 

 increasing for the locality, the minus sign meaning of course the reverse. 

 It will be noticed that the charts give considerably smaller values, and 

 in the last case values of reversed sign. The large changes and the 

 rapid variation with geographic position are to be especially noted. 



The errors of the charts in magnetic inclination reach a maximum of 

 about 3 degrees and in horizontal intensity of a unit in the second deci- 

 mal C.G.S. J. A. Fleming. 



TERRESTRIAL MAGNETISM.— Comparisons of magnetic observa- 

 tory standards by the Carnegie Institution of Washington. J. A. 

 Fleming. No. 1. Journal of Terrestrial Magnetism and Atmos- 

 pheric Electricity, 16: 61-84, pi. IV. 1911. No. 2. To appear in 

 same Journal. 



A summary is given of the intercomparison observations made at 

 various magnetic observatories throughout the world by the Depart- 

 ment of Terrestrial Magnetism for March, 1911. The accuracy striven 

 for is such that will be sufficient for ordinary magnetic survey purposes 

 and for this reason the intercomparisons are made with the usual field 

 instruments and methods and in the course of regular field work as 

 opportunity permits. Detailed descriptions of the various instrument s 

 used and their constants are given. The methods of observation fol- 

 lowed are according to the usual scheme of work at land stations, no 

 elaboration except in number being attempted. 



The corrections of each instrument used are all referred to the pro- 

 visional international magnetic standards of the Department. 1 These 

 corrections are determined by observations at Washington, which are 

 made practically under the same conditions as prevail in the field and 

 involve simultaneous observations with both the standard instrument 



1 Bauer, L. A., Preliminary note on International Magnetic Standard. Terr. 

 Mag., 12: 161- 165. 1907. 



