35 $ 
Mr. Robertson’s Obseroations , &c. 
The magnetical variation, ascertained by me, and laid down 
in my maps of Jamaica, is 6j- degrees east. 
I leave to others, better qualified than I am, to enquire, 
and to point out, what improvements natural philosophy may 
derive from this discovery ; which I hope may be an acqui- 
sition to science. 
I am afraid I have been too prolix. But the importance of 
the subject, and my desire to remove even the shadow of any 
doubt that might be suggested, will, I trust, be admitted as 
my apology. 
I have the honour to be, &c. 
JAMES ROBERTSON. 
