102 



APPENDIX. 



July the fecond, to try how far the megameter could be 

 depended upon, 1 obferved the altitude of the Carcafs's 

 maft 2° 23' 48"; the angle between the main-yard 

 and main-topfail yard, 0° 44.' 26"; hence the dif- 

 tance between the main-yard and main-topfail yard 



came out ■ 3i>75o feet. 



By meafurement it was found — 34>i25 feet. 



Difference 2,375 feet. 



>n 



The diftance between the two fhips, deduced from the 



altitude of the maft, was — 2457 feet. 



By the angle of the main and main-topfail yard, 



the diftance between them being 34,125 feet, 2640 feet. 



Difference 183 feet. 



Which is not more than the ftilps might have changed 

 their pofttion in the time of reading off' and fetting down 

 the firft obfervation before taking the fecond. 



« 



An error of ten feconds in the obfervation of the angle 

 fubtended by the maft at this diftance, would make an 

 error of two feet and three quarters in the diftance. At 

 the diftance of a nautical mile it would produce an error 

 of ftxteen feet. At other diftances the error decreafes as 

 the fquares of the diftances decreafe j and at other heights 

 it decreafes as the heights decreafe. 



Whenever 



