10 
Transactions of the Boyal Society of South Africa. 
In the summer 1912-13 observations were made in Bushmanland ; 
in addition, four repeat stations — Van Wyk's Ylei, Kenhardt, Aggennys, 
and Pella — were reoccupied ; the two latter stations had been first occupied 
in the summer of 1908-9, and the two former in the summer 1904-5. 
The instruments used were a dip circle by Dover No. 142, a unifilar 
magnetometer by Elliot No. 73, the property of the Eoyal Society of 
London, and in the summer of 1910-11 a magnetometer No. 164, lent by 
Professor A. Ogg to the author pending the arrival from England of 
No. 73, where it had been sent for repair. The constants for magneto- 
meter 73 are given below. This instrument had been used during 1908 
and 1909 in magnetic work between Cape Town and Cairo. At the end of 
this period the instrument was completely overhauled by the makers, and 
its constants redetermined at Kew in December, 1910. The previous 
determination of the constants of this instrument was made at Kew in 
August, 1902 ; their values at that date are given in the " Eeport of a 
Magnetic Survey," already referred to, and are repeated here for the 
sake of comparison. 
Constants of Magnetometer No. 73. 
Temperature Correction Induction Angular Value of 
t degrees Centigrade. Coefficient. one Scale Division. 
1902 I Collimator ) 0-000281^ + 0-05118^- 4-730 r-75 
1910 1 magnet 73a ) 0-000325^ + 0-05108^- 4-820 l'-75 
I Deflection magnet 73c { 6^^^ 
Brass Bar 73. 
Apparent Distance from Centre (in cms.) at 0° C. 
30 40 
1902 ) ^- ^ . ^ f u J- \ 29-993 39-994 
^r^^^l The distances corrected for bendmg... ■ 
1910 ) ° \ 29-993 39-991 
Log TT^ K. 
0°C. 10° C. 20° C. 30° C. 40° C. 
1902 3-47406 3-47416 3*47426 3-47437 3-47447 
1910 3-47349 3 47359 3-47370 3-47380 3-47401 
Auxiliary Brass Cylinder. 
Length. Diameter. Mass. 
1902 9-536 cm. 0-995 cm. 62-803 grm. 
1910 9-521 „ 0-994 „ 62 343 „ 
In addition to the magnetic instruments a 5-inch theodolite, No. 6084, 
by Cooke and Son, York, and a chronometer — Reid and Son, No. 1078 — 
were used. 
