Comparisons of Magnetic Standards, 1915-21 455 



at W; because of the magnetic character of W the results have not been utilized. It is, 

 however, interesting to note the general agreement of station-differences on W resulting 

 from these observations. Thus the two values of station-difference (N W) in decli- 

 nation resulting from these observations and those with the other instruments at sta- 

 tions A and B are +0'.6 and +0'.7 respectively, giving a mean value of +0'.7 as com- 

 pared with the 1915 value of -f-0'.9; the two values of station-difference (NW) in 

 horizontal intensity are +357 and +6I7, giving a mean value of +487, which is in 

 excellent agreement with the value of +527 determined in 1915. 



Series Previous to 1915. 



On December 13, 1905, January 4, 30, 1906, and March 12, 1906, Mr. G. Heimbrod, 

 observer of the Department, obtained 5 comparisons in declination between Tesdorpf 

 magnetometer No. 2025 and the Samoa Observatory sub-standard (Tesdorpf magne- 

 tometer No. 1975+0'.7) observing with No. 2025 at the declination pier in the absolute 

 observatory. Upon the completion of his field work in the Pacific islands with No. 

 2025 Mr. Heimbrod again on December 8, 9, 10, 13, 14, 1906, obtained 5 comparisons 

 at the Samoa Observatory. The results were: 



Tesdorpf No. 2025 Samoa (Tesdorpf magnetometer No. 1975+0'.7 = Potsdam") 

 = +2'. 45 and +2'. 30, respectively, or in the mean= +2'. 4. 

 Since (see Vol. II, p. 253) 



I.M.S.-Potsdam=+0'.2 

 we have: 



(a) I. M. S.-Samoa (Tesdorpf No. 2025)= -2'.2 



since all results at Samoa as published 6 and in manuscript are based on absolute obser- 

 vations by Tesdorpf magnetometer No. 2025 (magnet 12) with zero correction. 



For horizontal intensity, since the relative constants used for Tesdorpf magnetom- 

 eter No. 1975 are based on observations at Potsdam and since the relative constants 

 for No. 2025 (magnets 38 and 12), the "station-instrument" at the Samoa Observatory, 

 result from comparisons between Nos. 1975 and 2025 at Samoa, the Observatory stand- 

 ard is equivalent to that of Potsdam. For inclination also, since the standard at Samoa 

 is Schulze earth-inductor No. 2 without correction and which when originally com- 

 pared at Potsdam showed no correction on Potsdam standard, the Samoa standard is 

 equivalent to that of Potsdam. Since (see Vol. II, p. 253) 



I. M. S. - Potsdam = +0.00008// 

 and, for inclination, 



I. M.S.- Potsdam =+0'.2 

 we have: 



(b) I. M. S.-Samoa (Tesdorpf magnetometer No. 2025) = +0.00008//. 



(c) I. M. S.-Samoa (Schulze inductor No. 2) = +0'.2. 



Dr. Angenheister communicated in 1917, subsequent to the publication of Volume 

 II, the final Observatory values applying for the times of the various C.I.W. observa- 

 tions at Samoa in 1906, 1907, and 1911, together with a summary from all sources of 

 station-differences between the various piers and stations used for absolute observa- 

 tions. In view of the local natural and artificial magnetic-disturbances and magnetic 



" The declination correction of Tesdorpf magnetometer No. 1975 on Potsdam standard determined at Potsdam by 

 Dr. Linke in October 1904 was +0'.7 and in September 1907 was +0'.74 (see Vol. II, Res. Dep. Terr. Mag., P- 252). 



b Linke, F., und G. Angenheister, Ergebnisse der Arbeiten des Samoa-Observatoriums der koniglichen Gesellsi-haft 

 der Wissenschaften zu Gottingen. V. Die erdmagnetisehen Registrierungen der Jahre 1905 bis 1908. Berlin, 1911. 



