72 On the Rates of Chronometers. [No. 1. 



there can also be no doubt ; it is highly worthy of notice that on any 

 usual voyage from England, South of the Equator, and consequently 

 on a Brazilian, East India, China, or Cape voyage, the ship crosses near 

 to the spot (about Bahia, say in 13|- South Lat. and 35° West Long.) 

 where the Magnetic Equator crosses the line of No Variation ; or in 

 plainer words where there is no dip or variation ; whereas in England 

 the variation may be called in round numbers 24° and the dip 70°. 



The Chronometer is rated in England under these strong influences, 

 and every day's sail from England rapidly diminishes them to the 

 Magnetic Node above alluded to. They then increase again (but in an 

 opposite hemisphere) and for a short time, from Trinidad to a few 

 degrees East of the Cape where the line of dip of 60° intersects that 

 of 30° Westerly variation, they become high, but they rapidly decrease 

 again until the ship reaches the Bay of Bengal, where she again crosses 

 the Magnetic Equator and is not far from the line of No Variation, 

 having but a very feeble one of 2° or 3°. 



At Calcutta the Chronometer is rated under 2° or 3° of variation 

 only and 20° of dip, or about the mean of that last influence for the 

 whole voyage ; if it has any influence ? and in a city comparatively free 

 from iron as compared with those of Europe ; and it is carried but a 

 few hundred yards to place it in the boat which conveys it on board a 

 ship, of which no part of the homeward bound cargo is magnetic. 

 All these circumstances are no doubt in favour of the Calcutta rates ; 

 but whether it be the accidental causes, such as cargo, &c. or the 

 permanent ones such as the terrestrial magnetism which give this 

 advantage to the Indian rates it is difficult and at present indeed 

 impossible to pronounce. It will probably be found that both influence 

 the result. The fact, in which every confidence may be placed, is one 

 of the highest importance to the right understanding of this anomaly. 



In regard to the permanent causes, we have again to consider, in 

 reference to Messrs. Arnold and Dent's experiments alluded to at page 

 63, and the results stated by Mr. Northcote, how the arms of the 

 balance may have been placed with reference to the magnetic meridian 

 while rating, and how they would be placed on board the ship. The 

 first of these conditions probably varies at every maker's, according as 

 the house, or shop, or room used for rating, is placed ; but on board ship 

 the XII-VI. is usually, in the present day, and in large ships, placed 



