476 



each other a condition which is best secured by the 

 employment of the same instruments and the same 

 processes of experiment throughout. From this con- 

 viction I have limited the notice which has been here 

 taken, both of Captain Foster's experiments and of my 

 own, to the results obtained with the pendulums of the, 

 same form and construction as those which had been 

 employed by Captain Kater, and with which the same 

 methods of observation which had been first practised 

 by him were carefully preserved. I was myself pro- 

 vided with two other invariable pendulums, differing in 

 some respects in form from Captain Rater's, and attached 

 to a train by which their vibration was maintained and 

 the number of vibrations in a day recorded ; and these 

 were employed as a wholly distinct mode of experiment 

 at the greater part of the stations of my equatorial and 

 polar series. The record of the results with these pen- 

 dulums is given in full in the volume of my Pend. 

 Expts., pp. 237 287, where their close accordance is 

 shown with those of Kater's. In like manner, Captain 

 Foster was provided, in addition to the two Kater's pen- 

 dulums, with a copper and an iron experimental pendu- 

 lum (both differing in form from Kater's), which were 

 used at several of the stations which he visited, and the 

 results are given by Mr. Baily in the report already re- 

 ferred to, where they are shown to accord sufficiently for 

 general confirmation, at the stations where they were 

 employed, with those of Kater. It is always a great 

 advantage to an experimentalist to be provided with 

 a second and wholly distinct process of experiment, 

 though it may not be in all respects, perhaps, quite 

 so satisfactory as the one on which he principally 



