Dec. 1831. 



VESSEL EASY COMPASSES. 



45 



they close upon each other and receive vibratory undulations 

 from each shore ; augmented perhaps by the peculiar formation 

 of the bottom of that bay, the variation in depth, and the 

 effects of currents, which, when running over uneven ground, 

 or against the wind, alone cause a heavy swell; a striking 

 exemplification of which may be seen on the bank of Lagullas, 

 near the Cape of Good Hope. 



Though so deep in the water, our little vessel's movements 

 were uncommonly easy, and all our best timekeepers being 

 hung in particularly good jimbals, I had no fear of their rates 

 being altered, except by the effect of a change of temperature. 

 This was a point about which I was especially anxious, as 

 so much would depend upon the going of our chronometers, 

 and I did not then think that the motions of a ship affected 

 those instruments so little : as I have since proved to be the 

 case by trying them frequently in boats, or small craft of 

 only a few tons burthen. In her previous voyage the Beagle 

 was as easy a sea-boat as could be desired ; but, having raised 

 her upper deck, altered her stowage and trim, loaded her 

 more heavily, and sheathed her with two-inch plank, prepara- 

 tory to this second expedition, I had abundant cause to feel 

 anxious until the practical effects of such material changes 

 were ascertained. 



A little alteration was required near the compasses, for 

 owing to some ill-placed iron- work they did not quite agree ; 

 but, after this change was made, we were gratified by finding 

 four first-rate compasses, three fixed for steering, and one for 

 bearings, agree precisely. Another source of satisfaction, 

 connected with the compasses, was the knowledge that they 

 were not affected, unless in a very trifling degree, by local 

 attraction : for while lying in Barn-pool we swung the vessel 

 in order to ascertain its quantity, but were agreeably surprised 

 to find that none could be detected amounting even to one 

 degree. This was attributed to her having only brass guns ; 

 and to some very large iron davits for the quarter boats, 

 which vs^ere placed rather closely abaft and above the com- 

 passes, and perhaps counteracted the effect of iron in the hold^ 

 which was so much more distant. 



