1851.] On the Rates of Chronometers. 71 



2. Effect of the ship's local attraction, from her iron- work and 

 guns upon a polarized balance, in a man of war ? 



3. Effect of the cargo and iron work in a merchantman ? 



4. Vicinity to or bearing of, or direction of ship's head in regard of 

 the magnetic poles, augmenting the effect of terrestrial magnetism in any 

 ratio more than a direct one as the latitude is increased ? 



5. Distance from the magnetic equator? 



6. Opposite effects of terrestrial magnetism in Northern and South- 

 ern hemispheres ; so much (three-fourths) of the voyage to India being 

 performed in the Southern hemisphere. 



7. Difference of cargo out and home. (Accounts for rates being 

 more permanent homeward.) 



8. Whether there be not a local magnetic effect in London, Liver- 

 pool and in all great cities and towns ? arising from the enormous 

 masses of common and polarized iron in them?* a minute one of 

 course, but sufficient to cause a variation of rate ? We have com- 

 paratively very little iron at Calcutta ? 



Let us consider these conditions separately : — 



1. Carrying the Chronometers on board. Except where the Chro- 

 nometer is regulated near the docks, no doubt many chances of deranged 

 rates may arise from this source ; for between the jolting of a convey- 

 ance and the obstructions from passengers if on foot, the conveyance of 

 a box Chronometer is always a delicate and a difficult undertaking in 

 the streets of London or Liverpool. 



2 — 3. The effect of the ship's local attraction and of her cargo we 

 have already considered, and the facts now brought forward seem to 

 place it most unequivocally and beyond any doubt as one of the leading 

 causes of the irregularity. 



4 — 5. Magnetic poles and Magnetic Equator, Assuming that 

 terrestrial magnetism affects the balances of Chronometers, of which 



* All iron which remains long in a vertical position as a rail or the bar of a 

 window, becomes magnetic. There are millions of bars of iron so placed in London, 

 to say nothing of as much more in other positions ; the railings are, it is true, of 

 cast iron, which affects the compass least ; but their prodigious number and with 

 those which have stood from a quarter of a century to a whole century or more, 

 their increased magnetism ; which must go on to saturation, one would suppose ? 

 may place them as high as wrought iron or blistered steel. 



