MAJOR SABINE ON TERRESTRIAL MAGNETISM. 153 
« Hobart Town, May 21st, 1838: at the Stone in the Government Garden: 10 
vibrations in 50-033 seconds : therm. 63°-5. Observer, Captain Charles Drinkwater 
Bethune, R.N. 
“ Hobart Town, July 18th, 1838: Government House: 10 vibrations in 50-28 
seconds : therm. 57°-25 : dip, observed at the same spot with two of Mr. Fox’s instru- 
ments, 70° 31'-5. Observer, Commander John Wickham, R.N.” 
The correction for differences of temperature at the times of vibration of this needle, 
experimentally determined, is found by the formula 
T - V = -0003 T (t - f ) ; 
in which T' is the observed time of vibration corresponding- to the actual temperature 
t', and T the corrected time corresponding to the standard temperature t. 1 he cor- 
rected times of vibration at 60° Fahr. are as follows: 
Dublin 57'89 seconds. 
Cape of Good Hope 49'97 
Hobart Town, January 1837 • • 49-82 
Hobart Town, May 4, 1838 . . . 51-07 
Hobart Town, May 21, 1838 . . 49‘98 
Hobart Town, July 18, 1838 . . 50‘32 
Whence the values of the intensity are as follows, Dublin being 1*399* : 
Cape of Good Hope . . . 1*008 
Hobart Town 1-810 
The values determined by Captain FitzRoy in 1836'f~ were, 
Cape of Good Hope . . . 1*014 
Hobart Town 1-817 
L. 
Mr. Fox’s series of intensity results in France, Switzerland, and Germany, were 
obtained in the summer of 1838, with a four-inch needle deflected by the weights 
specified in the subjoined Table. The angles are half the sum of the deflections to 
the right and to the left, and are corrected for temperature at the rate of 2' for one 
centesimal degree, determined experimentally for the actual angles. In reference to 
these observations, (and to those of the dip in the Table in page 1 37-) Mr. Fox re- 
marks, that he always waited till the needle was at rest, and then repeatedly moved 
it, by turning a little the concentric disk and bracket from behind, reading off again 
and again when the needle had settled after the application of gentle friction. This 
he generally did at least three times before he noted the results, so that in fact the 
* Magnetic Survey of the British Islands, British Association Report, 1838, p. 191. 
t Variations of the Magnetic Intensity, British Association Report, 1837. 
MDCCCXL. X 
