and Intaia'ity of the Magnetic Needle. 361 



zontal needle, and the least that ought to take place in the 24 hours, 

 and this is precisely the time that the minimum intensity is recorded 

 to take place. At 10^ 40"^ p. m. we ought, in like manner, to have 

 the greatest intensity, because then the sun will be again on the meri- 

 dian, but its tendency will be to increase the magnetic colat., and, con- 

 sequently, to diminish the dip. We have no ^stinct account of the 

 intensity at this hour, but at 9^ 30™ v. m.* it is greater than at any other 

 hour recorded ; we may, therefore, I conceive, fairly state this as a con- 

 firmation of the agreement of the hypotheses with observations on these 

 cases of intensity. 



Again, at about 3^ 40™ p. m.j we have seen that the sun is to the 

 west of the magnetic meridian, the needle ought, therefore, at this hour 

 to have its greatest westerly bearing. This hour agrees very well with 

 a number of recorded observations, but, in the recent observations by 

 Colonel Beaufoy, the maximum is said to happen at 1^ 30™, at least 

 this was the time at which he always recoiile<l his noon observations. 

 Here, therefore, is some discrepance in time ; but the motion of the 

 needle is nearly suspended for some considerable time about this part 

 of the day, and the whole amount is so very small, that I can by no 

 means admit this as an objection to the hypotheses. It is only by a 

 very great number of hourly observations that the exact time of the 

 maximum can be deduced ; and where these are most numerous, the 

 time is variously stated from 2^ to 4^ p. m. We have no good record- 

 ed experiments during the night in London ; it is only generally said, 

 that the motion ot the needle is less to the eastward in the night than 

 to the westward in the day, and this ought to be expected from the 

 hypotheses, for the sun will pass during the night 30° farther from the 

 pole than in the day, and its effects, of course, ought to be proportion- 

 ally less. Upon the whole, therefore. Lieutenant Foster's hypothesis is 

 by no means at vaiiance with our recorded observations in London. 



Let us now submit it to a similar test witii the Port Bowen observa- 

 dons. 



* See Mr Christie's - Paper on the Effect of Temperature, icC—PAiA 

 Tmm. for 1824, ^ 



