Comparisons of Magnetic Standards, 1915-21 



465 



gating inertia change of No. 25. As will be seen from Table 20B a wide range of values 

 was covered both in the Northern and in the Southern hemispheres. The adopted 

 relation of C. I. W. to I. M. S. in horizontal intensity as indicated is from a least-square 

 reduction of the data given in Table 20B on the assumption that the change in inertia 

 was linear with time; the small range in the differences between values of AH/H computed 

 by the resulting formula and actually observed values justifies the assumption that the 

 inertia change was a linear one. 



As regards the standard in inclination the evidence of field comparisons from earth- 

 inductors is such as to leave no doubt as to the maintenance of a constancy of correc- 

 tion for all Values of inclination well within the error of observation. As regards the 

 correction on standard for dip circles, the detailed investigation and report on pages 

 359-371 shows the dip circle to be inferior to the earth inductor as an instrument of 

 precision even when every care is taken to obtain frequent comparisons at different 

 values of inclination. 



Table 20B. Comparismis 0/ ( '. /. 11". MagnetmneU 1 A ... -'}, 1914-191 S 



Date 



Approximate 



Com- 

 pared 

 with 



No. sets 



(I.M S. C.I.W. No. 25) 



W't 



Ml 



W't 



AH 

 Obs'd - 



ti 



A 



computed 



Jan. 29, 30, Feb. 2, May 16, 



1914 



Julv 7, S, 9, 1914 



July 23, 1914 



Aug. 28, 29, Sep. 9, 1914. 



Nov. 6, 7, 9, 1914 



Nov. 18, 1914 



Feb. 2, 3, 1915 



March 29, 1915 



May 27, 28, June 3, 4, 5. 1915 

 July 22, 23, 24. 26, 11915. . 



\ n 9, 10, 11, 12, 15, 1915 



Nov. 26, 1915. 



Nov. 29. 191.5 



Apr. 4, 5, 6. 7, 17, 1916 



July 20, 21, 22, 1916 



Sep. 29, Oct. 4, 1916. 

 Mar. 13, 14, 15, 16, 1917. . 

 Oct. 24,25,26, 27, 29, 1917. 

 Feb. 28, Mar. 12, 14, 1918. 

 June 17, IS, 21, 24, 25, 191S 



^Washington, .4, ('. and! 

 I D 



Hammerfest, .4 and B 



Hammerfest, B 



Reykjavik, A and E . . 



Washington, Sm and V,,, 



Washington, Nm and O 



Washington, Nm 



Colon, .1 and B 



Honolulu Obs'y. A and B 



Dutch Harbor, .4 and B 

 /Christchurch, brain 

 \ pipe and iarrah peg. 

 f Christchurch, absohil* 

 1 house and brass pipe 

 /Christchurch, peg and 



\ pipe 



/Christchurch, peg and 

 \ pipe 



Sumay (Guam), .4 andi? 



Goat Island, .4 and B. 



Pilar Obs'y, E and F. . 



Pilar Obs'y, E and F. . 



Lima, B and C 



Washington, N and S m 



- 2 



- 2 

 -44 



- 5 



- 5 



- 5 

 + 5 

 + 10 

 +16 



+ 17 

 + 17 

 + 17 



+ 17 



+ 2 

 + 18 

 + 

 + 

 + 9 



- 5 



.192 



.117 

 .117 

 .118 

 .191 

 .191 

 .190 

 .322 

 .290 

 .209 



.224 



.224 



.350 

 .250 

 .255 

 .254 

 .302 

 .188 



+71 



+77 



+77 

 +77 

 +71 

 +71 

 +71 

 +36 

 +40 

 +66 



-68 

 -68 



-68 



+ 14 

 +6: 

 -26 

 -26 



- 1 



+71 



-0.6 

 -1.0' 

 -0.6 

 -0.5 

 -0.8 

 -1.0 

 -0.2 

 -0 1 

 -0.2 



+0.1 



+0.3' 



+2.2' 



-0.5 



0.0 

 -0 2 

 -0.1 

 +0.4 

 -1.1 

 -0.8 



11 



5 

 1 



+0.00004 



-0.00006 

 +0.00025' 

 -0.00003 

 -0.00014 



II KM 



ii 00029 

 -0.00006 

 -0.00010 



-0.00015 

 -0.00036' 



-0.00039 



-0.00061 

 -0.00056 

 -0.00074 

 -0.00075 

 -0.00106 

 -0 00110 



-0.00004 



-0.00007 



+0.00025 



0.00000 



-0.00006 



-0.00020 

 -0.00011 

 +0.00017 

 +0.00016 



+0.00019 

 -0.00001 



+0 . 00006 



-0.00008 

 +0 . 00002 

 - 00004 

 +0.00013 

 -0.00011 

 -0.00013 



Adopted weighted mean values for (I. M. S.- 



I. W. No. 25) . 



-0'.3 



+0.00008 -((1914.22) 0.00026 



iC. I. W. standard magnetometer No. 3; see pages 7 and 10 for constants and corrections on I. M. S. 

 > See pages 7 and 10 and Table 20E for constants and corrections on I. M. S. 

 These values result from observations without exchange of station. 



C. I. W. magnetometer No. 26 is the sub-standard instrument of the Department and 

 has been used for comparison work at a number of observatories. The following ex- 

 tracts from an extended study of its constants by Mr. H. W. Fisk are, therefore, 

 given as a gage of the precision obtainable with field instruments. The series of com- 

 parison observations, four at the Standardizing Magnetic Observatory, Washington 

 (S. M. O.), one at Cheltenham, and one each at four English observatories, viz, Kew, 

 Greenwich, Stonyhurst, and Eskdalemuir. In making this study the ratios of the sines 

 of the deflection angles at the different deflection-distances, r, are frequently employed. 



and are abbreviated for convenience, thus: S n = 



sin u 2 



sm u 



and Sn = 



sm u 3 

 sin u. 



