( 77 ) 
like Circumftances, as to the Weather, it feems tome 
as if the Virtue of the Needle was not always of 
equal Strength. Sometimes feveral Obfervations 
would agree exceedingly well ; at other times the 
Card would Hand indifferently any where within a 
Degree or more of its Meridian ; and this I obferv'd 
in feveral Cards. I found another Circutnftance 
which furprized me much : The Card would fome- 
times differ about two Degrees from it felf betwixt 
the Morning and Evening of the fame Day •, and this- 
Difference would continue as it were regularly for 
feveral Days, then vanifh for a Week or more, and 
afterwards would return and continue as before. 
The greatnefs of this Difference, and the near Agree- 
ment betwixt the Obfervations made in the fameFore- 
noon, or Afternoon, amongft themfelves, will not give 
me room to fufped that it proceeded altogether from 
an Error in obferving. I own I cannot account for it, 
but whatever be the Caufe thereof, the Error was 
always the fame way ; that is, the Wefterly Variati- 
on in the Morning would be lefs than in the After- 
noon. I carefully examined if this could be any 
ways owing to the Inftrumenf, or to any Iron near 
the Place where it was ufually fet for Obfervation j. 
but I was fully convinced it could proceed from nei- 
ther. I know not whether any fuch Obfervations as 
thefe have been made before j but I think it would 
not be unufeful, if thofe who have proper Inftru- 
ments, and are fufficiently skilled, would communi- 
cate any thing of this kind that may occur. 
It now appears that the Numbers in the 'foregoing 
Table cannot be ftriOJy accurate ; but I think the 
Error can fcarceany where exceed half-a Degree ; f° r 
