2 66 Gen. Roy’s Account of 
three or four inches in diameter, and the largefl but fix orfeven. 
Augmented to nine or ten inches, exhibited on the top of one 
high hill, and obferved from the top of another, when there 
is no moonlight, and no rain or fog, they would probably be 
feen eighty or a hundred miles. In fhort, wherever the moft 
faint looming of the land in a very clear day can be dilcei ned, the 
lights, from their extraordinary brilliancy, would undoubtedly 
be feen in a dark night, when the air was perfectly clean 
Hence, it will readily be conceived, how eafily and accu- 
rately any trigonometrical operations that might be carrying 
on in England and Ireland at the fame time might be conneded 
with each other, by means of thefe lights, alternately exhibited 
and obferved, for in Ranee, on Brach-y-pwl Point, Holyhead 
Hill, and the Ife of Man , on one fide ; and again on the 
mountains of Wicklow, hill of HoWlh , and mountains of Mourne, 
on the other. 
In the Paper of 1787, and again in this, we have had occa- 
fion to remark on the improbability of being able to determine 
the differences of longitude, by the inflantaneous explofion of 
light, fo accurately as by angular meafurement with a fine in- 
flrument, applied as it has been 111 the recent operation. Put 
lince, undoubtedly, there will be different opinions on this 
head, it will be very proper that both modes fhould be tried, 
that the refults may be compared. 
To the eaftward of Greenwich, the Ration for explofion 
might be taken at Montlambert, Fienne Windmill, or at Folk- 
fone Furnpike, in order to render the diftance of the extreme 
Rations as great as poffible. Any of thefe points would be 
vifible from Crowborough Beacon, which would become the 
Ration of the Englifh aflronomer with his clock and inflru- 
ments. That of the French aRronomer would of courfe be 
- • taken 
