ON THE MAGNETIC SURVEY OF SCOTLAND. 



177 



It will be seen how nearly this value coincides with that given by the 

 Scotch survey instrument. 



No correction of any kind has been applied to the observed values of total 

 force at the different stations. 



At some of the stations vibrations only were taken. In such cases, it is 

 necessary to know the moment of the magnet at the time of observation, in 

 order to eliminate it from the product m X. This may easily be found ; 

 for every complete observation gives us a value of m, as well as of X. 



These values of m will be found to vary with the time, because the magnet 

 is gradually losing magnetism, and in consequence its moment is slowly 

 diminishing. If, therefore, we combine these values together, each year 

 separately, by the method of least squares, we shall be enabled to express 

 the magnetic moment in terms of the time. We have used this method to 

 find the value of X in those cases in which vibrations alone were taken ; but 

 for those in which both vibrations and deflections were observed, X has been 

 determined by means of the two equations thereby furnished. 



In the following Table are exhibited the values of X obtained by both these 

 methods, and also the value of the total force for the different stations 

 obtained from the observed values of horizontal force and dip, by means 

 of the formula — 



horizontal force 



Total force =• 



cosine dip 



Table IX. 



Station. 



Date. 



mX. 



Greenwich 

 mean time 



of ob- 

 servation. 



X 



Greenwich 

 mean time 



of ob- 

 servation. 



Calculated 

 value of m 



Total 

 force. 



Makerstoun .... 

 Gretna 



Dumfries 



Newton Stewart 



Stranraer 



Ayr 



Lamlash 



Helensburgh.... 

 Lochgoilhead . 



Ardrishaig 



Oban 



Corpach 



Fort Augustus . 



Inverness 



Banff 



Peterhead 



Aberdeen 



Kintore 



Alford 



Braemar 



Pitlochry 



Dalwhinnie 



Larbert 



Edinburgh 



1859. 



1857. 



Aug. 10 



15 



15 



17 



19 



19 



20 



22 



25 



28 



29 



Sept. 4 



7 



8 



9 



11 



15 



17 



17 



19 



21 



22 



24 



28 



29 



Oct. 1 



5 



1-7248 

 1-7225 



1-7286 

 1-7138 



'i-riio 



1-7000 

 1-7061 

 1-6662 

 1-6805 

 1-6740 

 1-6653 

 1-6541 

 1-6312 

 1-6255 

 1-6319 

 1-6320 

 1-6318 

 1 -6329 

 1-6520 

 1-0440 

 1-6657 

 1-6521 

 1-6550 

 1-6565 

 1-6853 



1 p.m. 

 122 " 



11 55 A.M. 



•14391 

 •14382 

 •14389 



h m 



•14464 

 •14460 



•14561 

 14493 

 14846 



14761 

 14829 

 14946 



•15171 

 •15126 



•15093 

 ■14919 

 14943 



•14924 

 •14869 



•49777 

 •49767 



: 49735 



•49697 

 •49669 



•49644 



•49026 

 •49606 



3-4620 



3-4604 



3-4714 



3-4424 



3-4381 

 3-4171 

 3-4310 

 3-3500 

 3-3789 

 3-3677 

 3-3511 

 3-3267 

 3-2822 

 3-2733 

 3-2846 



3-2856 



3-2891 

 3-3276 

 3-3168 

 3-3553 

 3-3272 

 3-3349 

 3-3378 

 3-3974 



N 



10-548 



10-505 



10-519 



10-523 



10-519 

 10-548 

 10595 

 10-538 

 10-531 

 10-575 

 10-560 

 10-702 

 10047 

 10067 

 10-596 



10-582 



10-543 



10-550 

 10-599 

 10-587 

 10-535 

 10-598 

 10-552 

 10-536 



