Sequel of (he Exper'wwiits upon the Magnetic Needle. 257 



time tliGV are on shore ; and if the rates are ascertained on board, 

 the chroiioineters should always be kept in the same place, and 

 also in the same position with respect to the ship ; for I have 

 but little doubt that, upon an accurate trial, a chronometer will 

 be found to change its rate, more or less, according as these cir- 

 cumstances are attended to. If these precautions are not taken, 

 land will apjjcar to be considerably to the westward of its true 

 position : this is particularly exemplified in the observations of 

 the Hon. Captain Phipps; from which nearly the whole line of 

 coast on the west side of East Greenland has been placed nearly 

 \\° too much to the westward, by reason of the acceleration of 

 his chronometers : the same circumstance would have occurred 

 with the chronometers in both of the ships Dorothea and Trent, 

 in the late voyage, had not the longitude been otherwise deter- 

 mined. It is therefore highly requisite that attention should be 

 paid to a circumstance so much connected with the improve- 

 ment of geography as well as the safety of the seaman. 



The foregoing paper is followed by an Appendix containing 

 Tables of Rates furnished by Mr. Coleman, teacher ofnaviga- 

 tion, and embrace observed rates in different voyages from 1802 

 to 1820 inclusive, corresponding very much with Mr. Fisher's, 

 and tending to confirm his general inferences. 



XXXIX. Sequel of the Experiments on the Action of the Vol- 

 taic Pile upon the Magnetic Needle. By M, Boisgeraud 

 Jan. 



[Concluded from p. 206.] 



A THINK it useful to make known an illusory phaenomenon which 

 tlic Voltaic aj)paratus I made use of presented. I took a very 

 fine bilk thread ; I attached it to a fixed point by a small |)artlcle 

 of wax. 1 took another very small particle of wax, which I fixed 

 to the other end of the thread, in such a manner as to form a 

 pendulum with it. I afterwards pressed the latter piece of wax 

 on one of the poles of a magnetised steel wire which remained 

 suspended. The other ])ole was rubbed with a little grease, so 

 that I could make adhere to it horizontally a small needle of 

 Spanish wax or silver. This arrangement, it will be observed, has 

 some analogy with the electroscope of Coulomb. The object of 

 it was to indicate the action of the conducting wire on the faces 

 of the needle. The following arc the deceptive pliLcnomcna which 

 it presents. 



A magnetised bar which I held in my hand appeared con- 

 stantly to attract, by its north pole, the south face of the sus- 

 pended needle ; the south pole apjjcarcd cc|ually to attract the 



Vol. Ul. No. 27(i. ylpiU 1 S2 1 . K k north 



