482 



of Colonel Smythe's observations, Major-General Sabine is desirous 

 of drawing the attention of the Fellows to the thoroughly business-like 

 manner in which Colonel Smythe has performed this useful service 

 and to the illustration which it affords of the advantages anticipated 

 by M. Gauss from the establishment of the British Colonial Magnetic 

 Observatories that "they would become schools for many good ob- 

 servers who would subsequently extend their activity over a wider 

 range, and would contribute to arouse, to nourish, and to extend to 

 other parts of natural knowledge that desire for the greatest possible 

 accuracy in observation which was formerly met with only in Astro- 

 nomy and in the higher Geodesy." (Letter to Sir John Herschel 

 printed in the Reports of the British Association for the Advance- 

 ment of Science for 1845, p. 45.)] 



The accompanying observations were taken at a wooden house 

 erected for the purpose on a clay soil 106 feet above the mean level 

 of the sea, and distant 265 yards West (19 07' S.) from the spot on 

 the beach where I have been informed Captain Denham's observa- 

 tions were made. The latter spot is on volcanic rock thinly covered 

 with sand and grass, close to the base of the low rocky promontory 

 on \^hich Commodore Wilkes, U.S.N., set up his Observatory. 



Declination. The values of this element, deduced from A.M. and 

 P.M. observations of the sun's azimuth, differ by about 10'. As the 

 several determinations in each position agree very well, the difference 

 is treated as instrumental error, and the mean of the two results 

 taken as the true value of the Declination. 



Inclination. The individual readings of the needles in the various 

 positions differed considerably. The means, however, accord. 



Intensity of the Force. By comparison of the time of vibration 

 in December 1860 and April 1861, the suspended magnet is per- 

 ceived to have lost force. During the interval, it remained in its box 

 perfectly undisturbed. The value of ?r 2 K used in all the calculations 

 is the same, as there was no means of ascertaining its temperature 

 corrections. It was deduced from a series of vibrations with and 



without the gun-metal cylinder No. 6, in December 1860, after the 



p 

 conclusion of the observations for Intensity. The correction 1 



has not been applied. 



