Comparisons of M.\gnetic Standards, 1905-14 



219 



results on account of change in the induction correction with H and because of change in the 

 constant with temperature, the perfect agreement of the Brunner magnetometer with the 

 C. I. W. standard must be regarded as fortuitous. 



The change in the declination-correction on the C I. W. standard of the Echassoux 

 magnetometer (Magnet I) from 3'. 6 (January) to +0'.3 (December) may have to be 

 attributed to instrumental changes. However, the declination correction for the Brunner 

 magnetometer also changed from +2'.5 (JanuarjO to V.2 (November-December). 



Table 2C. Results of Inclination Comparisons at the Algiers Observatory, January and December 1912. 



'All are referred to station O; O = M0'.2. 



We thus obtain [C. I. W. Algiers (Laderriere D. C, needles I and II)] equal to 3'.2 (Jan. 

 1912), and equal to 7'. 3 (Dec. 1912). It would appear that there has been some change 

 in the Observatory dip circle, especially in needle II, between January and December 1912. 

 In view of the uncertainties in the results due to various changes, the reductions to 

 I. M. S. (see p. 273) are omitted. 



NO. 3. ALIBAG OBSERVATORY, NEAR BOMBAY. INDIA. 



The results of comparisons of standards given below were obtained incidentallj' to other 

 duties. The observations made March 22-24, 1911, at the AUbag Observatory, by Observer 

 W. H. Sligh, of the Department of Terrestrial Magnetism, were secured bj' him while pass- 

 ing through Bombay in the course of a magnetic field trip. He used C. I. W. magnetometer 

 No. 7 and Dover dip circle No. 202 with needles 1 and 2. W. V. Nene, of the Observatory, 

 made observations simultaneously with him, using Cooke magnetometer No. 7 and dip 

 circle No. 160, made bj- the Cambridge Scientific Instrument Company. 



Two stations were occupied in the absolute observatory, which are designated as 

 Upper Pier (U) and Lower Pier (L). U is the central sandstone pier, with marble top, on 

 the second observing floor of the building, and is the pier regularly used for observations of 

 declination and of horizontal intensity; the one directly south of it is a wooden pier (C/,) and 

 was used for the dip-circle observations. The earth-inductor observations are made on the 

 pier about north of U and the accompanj'ing galvanometer is mounted about 3.5 feet 

 northwest of U. L is the solitary stone pier, with marble top, on the first observing 

 floor of the building; it is used for D, I, and H observations; the Observatory published 

 values are all referred to U. 



The corrections to be applied to the observations at L to refer them to U, according to 

 the data given by the Observatory, are: -j-VA for declination (i. e., east declination is 



