188 histructionsfor the Scientific Expedition 



if any, should be noticed, though it is at present believed that they 

 have no influence. 



During an earthquake in Siberia in 1829, the direction of the 

 horizontal needle, carefully vratched by M. Erman, was uninflu- 

 enced ; should a similar opportunity occur, and circumstances per- 

 mit, it should not be neglected. 



Should land or secure ice be found in the neighbourhood of the 

 magnetic pole, every attention will of course be paid to the procuring 

 a complete and extensive series of magnetometric observations, which 

 in such a locality would form one of the most remarkable results of 

 the Expedition. 



2. Figure of the Earth. 



The Expedition being provided with invariable pendulums, with all 

 the necessary apparatus for determining the length of the seconds 

 pendulum, it will be highly desirable to have this important observa- 

 tion made at several points, especially in high southern latitudes, 

 and generally speaking at points as remote as possible from those 

 at which it has already been determined. The selection of these 

 must depend on local circumstances, as regards convenience for 

 landing the instruments and executing the operations, as well as on 

 the times of arrival at the several points. 



It would also be desirable, if a convenient opportunity occurs, to 

 swing the pendulums on the top of some high mountain ; in which 

 case they should also be swung at the foot of the same mountain, in 

 order to determine the difference produced by the elevation, or other 

 eff'ect of the high land. 



Another experiment which it would be desirable to make, is to 

 swing the pendulum on a large field of fixed ice, as far from the 

 land as possible ; and likewise on the nearest shore to such position. 

 In all these cases more than one pendulum should be used ; and 

 at least three knife edges should be employed, in order to guard 

 against any unforeseen anomaly that may arise. 



It is scarcely necessary to state, that the direction of the line of 

 motion, with respect to the magnetic meridian, should be noted at 

 each station. 



3. Tides. 



With regard to tides, it is not likely that Capt. Ross's other em- 

 ployments will allow him to pursue observations on that subject 

 with any continuity ; nor is it desirable that he should do so, except- 

 ing he were able to carry on his observations to a much greater ex- 

 tent than is consistent with the nature of the Expedition. There 

 are, however, certain objects which may be answered by occasional 

 and detached observations, which may be briefly stated. 



1. At all stations on the coasts visited, and especially at all de- 

 tached islands in the middle of wide seas, it is desirable to obtain 

 the correct establishment of the place, or mean lunitidal interval. 

 This may be done with tolerable accuracy by a few observations of 



