propofed trigonometrical Operation. 2 r ^ 
the repeated explolions of gunpowder in the open air, and 
found to contain 41618 toifes, equal to 443^4.4 fathoms. Bv 
attending to the table it will be feen, that the error in excels 
of M. Bouguer’s theory, on the length of this degree trio-ono- 
metrically meafured, amounts only to 19 fathoms, which is 
little more than T ~th part of a fecond of time. 
In fixed Obfervatories, where able aftronomers have been for 
many years employed in repeating their obfervations of the 
heavenly bodies, it feems furprifmg, that any doubt fhould 
remain with regard to what is called the agronomical dif- 
ference of longitude, or, in other words, the difference of time 
between them ; yet it has been alledged, that an uncertainty 
of this fort exifts, even with regard to the fituation of Green- 
wich and Paris, which, reckoned by its extremes, extends to 
about 10 or 11 feconds, anfwering in the latitude of Green- 
wich to the enormous difference in ipace of between 1600 and 
1700 fathoms! But it will be conlidered as hill more won- 
derful, if between two Britifh Obfervatories, Greenwich and 
Oxford, which have heen long fupplied with great and coftly 
inhruments of the very beft kinds, there fhould remain an 
uncertainty in this refpedl of 2 or 3 feconds of time : for in 
the latitude of Greenwich 3 feconds correlpond to 477, and in 
that of Oxford to 474! fathoms. Thefe, however, are points 
which muff be left to the refpedtive aftronomers to fettle in the 
belt way they can ; and it is not to be doubted, that the Aflrono- 
mer Royal will throw a new and very fatisfa&ory light on the 
matter, in the Paper which he propofes about this time to lay 
before the Royal Society, along with M. Cassini’s Memoir, 
which, for that purpofe, has now been nearly two years in his 
polfelEon*. 
With, 
