1851.] On the Rates of Chronometers. 73 



in a line with the keel ; in Mr. Northcote's experiments however it was 

 placed at right angles to it, and against the side, (which side, is not said) 

 and this again throws much uncertainty upon the results, for the bolts, 

 which would be hidden by the lining of the Chronometer-room 

 or cabin, might have affected the balances. We may suppose the 

 balance to be so hung that, when at rest, the arms coincide with the 

 XII. and VI. hour marks. The line of the keel from the Channel to 

 the Magnetic Node in 13^° S. will generally be not far from a line at 

 right angles with the lines of variation, thus allowing this influence to 

 have its full effect whatever that may be ; and after passing this point 

 it will be at first, and until Trinidad is reached, nearly upon the lines of 

 variation, and then again gradually approach to a right angle with 

 them, not being perhaps at less than 45° till Amsterdam and St. Paul's 

 are passed ; after which it will be gradually approaching the magnetic 

 meridian with a very low variation, until the ship's arrival at Calcutta. 

 On the homeward bound voyage from India however the case is 

 different. The ship leaves Calcutta with Chronometers rated under very 

 favourable circumstances as regards terrestrial magnetism, and without 

 cargo to affect the rate, which is thus only disturbed by her local 

 Deviation,* and until near the tropic of Capricorn experiences but little 

 terrestrial variation, too weak indeed, as we may suppose, to affect the 

 balance, as it does not exceed 5° to 10°; though it is gradually becoming 

 stronger, and at right angles to the line of her keel, or the line of XII. 

 VI. Upon her crossing the southern tropic, say in 65° East, we may call 

 the variation 15° at right angles to the keel, and the dip 55°; and from 

 hence to past the Cape the variation is constantly rising to 30° and 

 nearly at right angles, but the Cape once passed the whole distance to 

 the latitude of 30° North and to the West of the Azores, is nearly upon 

 the magnetic meridians ! but at this point, with a high variation, the keel 

 (XII. VI. line) is again thrown gradually round as she passes the 

 Azores and until the ship's arrival in England is nearly at right angles 

 to the magnetic meridiau.f In the Appendix to Vol. II. of the Survey- 



* My friend Capt. Henning, of Messrs. Green's ship, the Alfred, has obliged me 

 with a note of his local variation (deviation) as observed in the Hooghly, and it 

 amounts only to about 5° on a mean. 



f And the Cape and Channel are the two points at which we so frequently hear 

 of accidents from the Chronometers being wrong. I mean of course blundering 



L 



