f tes i 
Tue ingenious Mr. Churchman of Philadelphia merits refpect 
for endeavouring to add fomething to the common ftock of 
knowledge, but I doubt the truth of his fyftem for the follow- 
ing reafons. The variation of the needle has been increafing 
here fince the year 1657, and the meafure of it this month, 
at Dublin, is 27 degrees 23 minutes wefterly, and in the year 
1794 we may expect it will be ftill greater ; but by Mr. Church- 
man’s Chart of the Northern Hemifphere, which is conftructed 
for that year, the variation meafures barely 1g degrees : At pre- 
fent it differs from the truth more than eight degrees, and if 
the following obfervations can be depended on, I may ven- 
ture to affirm the difference that year will be much more 
confiderable. 
It is now nineteen years fince I firft paid a ferious attention 
to this furprifing phenomenon, the change of the variation of 
the Horizontal Needle, and my experience ever fince has con- 
vinced me it is uniform at Dublin. This is the chief point, firit 
to be determined, and the next, which naturally follows, is an 
enquiry whether it be fo in every other place, or not: Here, I am 
confident, and hope to prove, it has varied, fince the year 1657, 
at the rate of about 12 minutes 20 feconds annually. The 
query is, What is its ratio elfewhere? This can only be difco- 
vered by general obfervations, as I mentioned before ; and until 
this be effected any idea of finding the /ongitude by the varia- 
tion mutt be delufive. 
' OcTOBER 
