Nassau New Providence July 4th. 1789
Sir.
Your established Character in the World as a Natural Philosopher
and Master of Science, being a Native of America myself (tho’
expelled by the Fortune of War from South Carolina) induces me to
address a Line to you on a Subject interesting to the World at
large but particularly to all maritime States. I shall esteem the
acknowledgment of the Receipt of this with your candid and free
Opinion thereon as an Honor conferred on Sir Your most Obedient
and most humble Servant
The Honble. Benjamin Franklin Esquire
By measuring Space by Time The Moon appears to Me to be at the
Distance of 36,313.845 Statute Miles from the Earths Center—Radius
of her Orbit 2 = 72627.69 Diameter of Ditto x 3.1426968 (The
true Proportion of Circumference to Diameter) = 228246.809 Miles
for the Circumference of Orbit 29.530851 Days to one
Revolution (= 235 migh?) = 7729.09689 Miles as the Diurnal
Motion of the Moon and supposing her to revolve round her own Axis
3.1426968 = 2459.383574 Miles for her Diameter. I go on the
Data that the Earths Radius is = 4000 Miles and Revolution in 24
Hours of our Time.
The Use I would recommend the above to would be to ascertain the
true Longitude of Places East and West of any fixt Meridian (for
which Purpose I have begun (tho a most tedious Business to
calculate the sines and Co-sines to 1¹, for 45º the 8th
part of Earths Circumference. As the lines of 45°, become the
Co-sines for the Remainder of Quadrant by squaring the former,
deducting the same from of Radius and taking the Roots of
Remainders for Co-sines which are the Sines for other Part. The
Sines by Logarithms are I think very untrue tho’ they answer for
small Distances. Such Table being compleat for real Time, If an
Observation be make on any fixt day when the Sun is in the
Meridian of Observer and the Moons Angle be ascertained to the
Earth’s Center by referring to the Table for Angle of Moon at fix
Meridian for that day The difference of Angle of Observation from
Tabulat Angle will be the Difference of Time and Distance And by
simple Proportion. As suppose from 0 in Scheme, you find the Angle
of Moon, as at Moon observed, and by your Table it should be in
your Zenith on due South The difference between the Time being
known Say As 10631.10636 Minutes in Quadrant of Moons Orbit :
3600' (=6 Hours Earths Quadrant) :: Difference of Time in Angle
: Min on Earths Surface Then As 3600' : 6285.3936 Miles in
Quadrant :: difference of Time : Miles in Longitude.
Suppose a Person at the Equator on any day when the Moon at any
fixt Meridian should be due South at Noon but by Observation
should be found to have an Angle which being corrected for Earths
Center as in the Scheme below as OE Moon observed = 65° from
Observer’s Zenith = 7678.021293 Minutes of Time They say As
10631.10636 : 3600' :: 7678.021293 : 2600' Time As 3600 :
6285.3936 Miles in Quadrant :: 2600' : 4539.45093 Miles But
Suppose the Observer to be in Latitude 25° North and find same
Angle of Difference look into Table for Cosine and you’ll find
3678.4313 1.5713484 = 5680.0971 Miles for Quadrant in that
latitude then say as 90° : 5780.0971 :: 65° : 4174.514572
Miles Quare if not the true Distance of Nassau in New Providence
West of such fixt Meridian.
Please excuse the want of Scholastic Terms as the Ideas are my own
without such Help, but from Mechanic Principles.
Quadrant of Moons Orbit at 25°. taken as a Globe of that Size
as a Proof for this Globe
Earths Radius 4000 1.5713484 = 6285.3936 Miles Quadrant And
the Proportion is easily demonstrated tho differing from all
before it.
Quare How can any Person know exactly in what Latitude He is in by
the usual method of taken the declination at a fixt Meridian when
perhaps she be from 50° to 90° West of same when the
Declination is varying constantly and at a considerable Rate and 6
Hours carries a Quadrant of this Globe to Meridian fixt.