46 Land Magnetic Observations, 1905-10 



Dover circle g. This circle is of type (a) and was used in the work in Africa by Professors Beattie 

 and Morrison; it belongs to the Royal Observatory, Cape of Good Hope. From the field 

 comparisons with standardized Dover circle 142, the following corrections were determined 

 and adopted for all observations with this instrument: needle No. i, 2'. 5; No. 2, 5'. 8; 

 No. 3, 4'.5; No. 4, 4'.o; No. 4 of circle 142, 4'.o; No. 6 of 142, 5'.3. The tabular 

 designations as used in the Table of Results are: 9.1234 and 9.12(46), the latter for obser- 

 vations when needles 3 and 4 of No. 9 were replaced by needles 4 and 6 of 142. 



Casella circle C. & G. S. 18. Of type (a), is the property of the United States Coast and Geodetic 

 Survey and was used during 1905 in the West Indies. The adopted corrections are: 

 needle No. 4, 1'.6; No. 5 of circle 172, 3'.!; No. 6 of 172, 3'. 5. The tabular desig- 

 nations are 18-4, and 18-4(56). 



Chasselon circle 20. Of type (c) , belongs to the Zi-ka-wei Observatory and was loaned the Depart- 

 ment for its earlier work in China. Owing to some magnetic impurity in the metal parts 

 of the instrument, the correction to standard for the needle used (No. 2, marked . .) shows 

 considerable range, varying practically linearly from +II' for the dip 30 north to 7' 

 for the dip 50 north. The tabular designation is 20-2. 



Chasselon circle 24. Of type (c) and the property of the United States Coast and Geodetic 

 Survey. As in the case of No. 20, there appears to be some magnetic impurity in the 

 metal parts of the instrument. The corrections to standard are the same for both needles 

 used, number I (marked .) and number 2 (marked . .) and are represented by the formula, 



/-A/ = -f 7'.5 +_ii'.8 cos (7 -f 36.9) 

 derived from numerous comparisons with standards by observers of the Department as 

 well as of the United States Coast and Geodetic Survey. The tabular designation is 24 12. 



Dover circle 33. Of the type (a), the property of the Zi-ka-wei Observatory and loaned the 

 Department for some of the earlier work in China. The correction of needle No. 14 to 

 standard is I'.i as determined from comparisons made at the Observatory with stand- 

 ardized circle 178. The tabular designation is 33-14. 



Lloyd-Creak Dover circle C. df G. S. 34. Type {b); the property of the United States Coast and 

 Geodetic Survey. The correction on standard of the mean of values observed with 

 needles Nos. i and 2 is 1'.9. The tabular designation is 34-12. 



Lloyd-Creak Dover circle C. &" G. S. J5 {Dover No. 168). Type {b); the property of the United 

 States Coast and Geodetic Survey; loaned the Department for use in the Galilee work 

 1905 to 1907. Early in 1906 the circle was modified in the instrument shops of the Coast 

 and Geodetic Survey, the original single deflection distance of 7.3 cm. being replaced by 

 two deflection distances of 7.9 cm. and 9.4 cm. The correction adopted for the mean 

 value obtained with needles Nos. i and 2 prior to the modification of the instrument 

 was 2'. 6. After the modifications, early in January 1906, and continuing until Decem- 

 ber 1906, the corrections adopted from least square reductions of results of comparisons 

 with land dip circles were as follows: 



Needle No. 2 FM = 12'. 8 -\- 14'. 2 cos I -f 4'.o sin I 

 Needle No. 5 of circle 163 FM = 2 .7 -f 4 .0 cos 7 2 .7 sin 7 

 or, for the mean of the two needles, 



FM = -7'.8 -f 9'. I cos 7 -I- o'.7 sin 7 

 Needle No. 6 of circle 163 was also used at San Diego at the beginning of the second cruise 

 of the Galilee during January and February 1906; the correction adopted for the mean of 

 needles No. 5 and No. 6 of circle 163 was 3'.6 for this period. In December 1906, 

 after repairs to needle No. i, it and No. 2 were used through July 1907, needle No. 5 of 

 163 being returned to its own instrument and the corrections adopted from least square 

 reductions of results of comparisons with land dip circles were for this period : 

 Needle No. i FA7 = +2'. 7 i'.4 cos 7 3'.6 sin 7 

 Needle No. 2 7^A7 = -fg .2 9 .4 cos 7 4 .8 sin 7 

 or, 



Needles Nos. i and 2 7"A7 = +5'.9 5'.4 cos 7 4'.2 sin 7 

 During the latter half of 1907 this instrument was used in land work in Canada; the 

 correction adopted from comparisons with standards, for the range of dip covered by this 

 work, was -Fo'.s for the mean value observed with needles Nos. i and 2. 



