106 Astronomical and Nautical Collections. 



is left to the discretion or management of the observer. The appa- 

 ratus has long been open to the public inspection in the Royal 

 Observatory at Greenwich. The reason that no results have been 

 obtained from it, is the failure of the clock-work by which it was to 

 be kept in motion, and which was intended to act by a single re- 

 coiling stroke at the lowest point of the vibration, but which was 

 not so executed as to comply with that necessary condition. But 

 this difficulty might readily be overcome by any person who would 

 undertake to make the experiments by means of coincidences, it 

 being only necessary for this purpose to be provided with a clock 

 with four different pendulums of different lengths, capable of having 

 their coincidences observed in the different places of the weight to 

 be employed. The mode of computation is shown in the Philoso- 

 phical Transactions for 1818. 



Captain Sabine doubts altogether of the perceptible effect of a 

 ship's magnetism on the rate of any good chronometer, and those 

 of Messrs. Parkinson and Frodsham he found altogether exempt 

 from it. Page 392. 



Captain Sabine has also given us the results of a multitude of 

 experiments for determining the variation in the intensity of ter- 

 restrial magnetism, page 460. He seems to have ascertained that 

 the agreement between the intensity and the magnetic latitude, as 

 computed according to the approximation derived from theory, is 

 more regular than the connexion between the dip and the intensity ; 

 but this is far from being an exception to the validity of the theory 

 in the form first published in this Journal, as might be inferred from 

 the manner in which Captain Sabine has stated it ; on the contrary, 

 it is more easily conceivable that local causes of disturbance should 

 affect the direction than the magnitude of the magnetic force in 

 any spot, as is obvious from the laws of the composition of forces ; 

 for the hypotenuse of a triangle, of which the legs are very un- 

 equal, differs very little in length from its longer side, though its 

 direction may be considerably different. 



The situation of the magnetic pole Captain Sabine finds it most 

 convenient to place in latitude 60° N., longitude 80°, or rather 

 78° W. He then finds the magnetic force, as computed by Dr. 



