462 



Special Reports 



Table 19B. Results of Horizonlal-InlensitylComparisons at the Watheroo Observatory, 1920. 



' All values are referred to N m ; N m = Sm1.0y. 'Half set; weight one-half. 

 Table 19C. Results of Inclination Comparisons at the Watheroo Observatory, 1920. 



1 All values are referred to N*; A r , = S+0'.24. 



Assembling the results, we have: 



(19) I. M.S.- Watheroo (C. I. W. magnetometer No. 7-0'.2) = +0'. I (1920). 



( 1 9a) I . M. S. - Watheroo (C. I. W. magnetometer No. 7 - 0.00054//) = + 0.000 1 5/Y ( 1 920). 



(196) I.. IVUS.- Watheroo (Toepfer inductor C. I. W. No. 2) = 0'.0 (1920). 



NO. 20. WASHINGTON, D. C. (DEPARTMENT OF TERRESTRIAL MAGNETISM), 



AND FIELD COMPARISONS. 



I. Maintenance of Constancy of Standards. 



The standardization of the field instruments used for the observatory comparisons 

 during 1915 to 1921, determinations of instrumental constants, and necessary experi- 

 ments, have been continued at the Standardizing Magnetic Observatory of the Depart- 

 ment at Washington as before. For an account of the methods and specimen com- 

 parisons, see pages 262 to 264 of Volume II. Some idea of the large amount of work 

 done in this connection can be readily formed by inspection of the results for the obser- 

 vations at Washington with C. I. W. standard magnetometer No. 3 and C. I. W. standard 

 Schulze inductor No. 48 in the Table of Results (see particularly pp. 71-76). Most 

 of these observations were made by Mr. H. W. Fisk, magnetician, to whose pains- 

 taking care and skill as an observer a large part of the credit for the successful establish- 

 ment of satisfactory magnetic standards used in the Department's work must be given. 



The question as to how closely various instruments after field work show constancy 

 of correction is of course a vital one. It may be said that the many comparisons of the 



