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On the Effects produced in the Rates of Chronometers by the Proximity 

 of Masses of Iron. By Peter Barlow, Esq. of the Royal Military 

 Academy. Communicated by John Barrow, Esq. F.R.S. Read 

 June 28, 1821. [Phil. Trans. 1821, p. 361.] 



It having been ascertained that during Captain Buchan's voy- 

 age to the arctic regions, in 1818, the rates of chronometers dif- 

 fered on board and on shore, and this change having been attributed 

 by Mr. Fisher to the iron of the vessel, the author felt desirous of 

 examining into the effects of the proximity of masses of iron upon 

 chronometers' rates, and of determining their causes. In this com- 

 munication he details the results of a variety of experiments and ob- 

 servations relative to the effects of iron on chronometers placed under 

 different circumstances in its vicinity ; whence he concludes, that it 

 undoubtedly does alter their rates, but that it does not necessarily 

 accelerate them, as suggested by Mr. Fisher; on the contrary, in 

 Mr. Barlow's experiments, it was generally productive of retardation, 

 much depending upon the direction of the balance in respect to the 

 iron ; and although the law of this influence has not been ascertained, 

 it is suggested as a practical conclusion, that on ship-board care 

 should be taken to keep chronometers out of the vicinity of any con- 

 siderable mass or surface of iron ; and as much of the iron of a ship 

 is concealed, Mr. Barlow thinks the best way of ascertaining the 

 best situation for a chronometer would be to set down a compass in 

 any place designed for it, and to observe and compare the direction 

 of a needle with that of the azimuthal compass on deck, while the 

 vessel is on different tacks ; and if the disagreement between the 

 two be very considerable, another place should be chosen. 



Lastly, as the power of the iron to disturb the chronometer resides 

 on the surface (as in the instance of the compass), and as we know 

 generally the distance and direction of a plate, such that its power 

 may be equal to the mean action of the iron of the vessel, we are 

 thence able to ascertain, before a chronometer is sent on board, 

 whether the effect of the ship's iron will be to accelerate or retard 

 its going. 



On the Peculiarities that distinguish the Manatee of the West Indies 

 from the Dugong of the East Indian Seas. By Sir Everard Home, 

 Bart. V.P.R.S. Read July 12, 1821. [Phil. Trans. 1821, p. 390.] 



The following are the principal differences pointed out by Sir 

 Everard Home as characterizing the Manatee of the West Indies 

 from that species of the Dugong, lately described to the Society, 

 from Sumatra. It differs externally in the shape of the tail, in hav- 

 ing neither tusks nor nails, and also in the form of its snout. The 

 teeth differ in number ; and though the general form of the skeleton 

 is similar, there are fewer vertebrae. The stomach differs in the 

 shape of the solid glandular part, and of the lateral pouches, but 

 both animals feed upon fuci. The formb of the teeth, however, in 



