MAGNiSTfC SURVEY OF GRBAT BRITAIN. 



145 



portion of magnetic force lost by the needle in the several in- 

 tervals. It will be seen that the loss, on the daily average, 

 progressively diminished ; and, excepting in the first interval, 

 namely, between the 4th and 15th June, was not of sufficient 

 amount to create much uncertainty in the results, after the ap- 

 plication of a correction assigned in the usual manner, viz. a 

 daily rate for each interval, obtained by dividing the whole loss 

 in an interval by the number of days which it contains. In re- 

 gard to the first interval, when the loss was considerable, and 

 where a correction applied on the above principle can scarcely 

 be supposed an exact representation of the facts, it fortunately 

 happens that the six included stations are all in Yorkshire ; 

 and thus, though an equable correction in this interval may 

 make the values of the intensity at these stations appear more 

 discrepant with each other than they otherwise would do, yet 

 their collective bearing on the position and direction of the 

 isodynamic lines is scarcely affected. 



By experiments with this needle in different temperatures, 

 Mr. PhiUips found -000090 the coefficient (a) of (t^t') in the 

 reduction for temperature ; which has been employed in re- 

 ducing the values in the column g.^g_g to a mean temperature 

 of 60°. 



Table XLVI. 



Observations at York, collected in one view, to show the loss of 

 magnetism sustained by Mr. Phillips's needle. 8 =:= 70° 48''8. 



cos 9 



sin (5-0) 



Interval, 

 Days. 



Average 



daily loss. 



June 3 & 5, 1837 



June 15 



Aug. 1 



Sept. 7 



Oct. 2 



Feb. 19 & 20, 1838... 



62-2 

 68-2 

 67-5 

 65-0 

 63-5 

 35-5 



15 24-9 



16 100 



16 46-2 



17 000 

 17 06-9 

 16 550 



0-96632 

 0-96254 

 0-95897 

 0-95747 

 0-95665 

 0-95530 



I 46 



j 38 

 I 25 



1 140 



•00378 

 •00357 

 •00150 

 -00082 

 •00135 



00034 

 00008 

 00004 

 00003 

 00001 



Mr. Phillips's observations at twenty-four stations in England 



are comprised in Table XL VII. : the values of ''"^.^ „ are re- 

 ' ' sine— y 



