STATION FOIKTER FOR MARITIME SURVEYS. 



?nd G, fhalJ be found upon the fiducial edge of its refpeaive Defcrlptlon and 



ufeof th- ^''*''"'* 

 pointer* 



pointer. The center will then be found at H, which may be "^« ""^^^ ^^^'^'^ 



marked by the fleel point. 



Rationale of the Procefs. When an obferver at H fees M 

 and A at the angular diftance of 22°. 40' from each other, he 

 muft himfelf (by Euclid III. 20,21.) be placed fomewhere in a 

 circle M A H, in^ which the line A M is the chord of twice 

 that angle. And fo likewlfe when he obferves M and G under 

 the angle 53°, 59' he muft be placed in another circle M G H, ' 

 of which 1^ G is the chord of twice that angle, Confequently 

 H muft be at a point common to both circles ; namely where 

 they interfea. The more direa the interfeaion the lefs will 

 the refult be affeaed by the errors of obfervation : — when the 

 interfeaions are very oblique, the refult will in praaice become 

 uncertain; and in the cafe where the two circles coincide 

 throughout, the determination by two angles will be no better 

 than by one; that is to fay H may be any where in that circle. 

 This laft cafe occurs when a circle drawn through all the ob- 

 jeas does alfo pafs through the ftation itfelf. 



In the figure already referred to H, denotes the weft garret 

 window of my houfe in Soho-fquare, and the letters A, G, and 

 M refpeaively denote the fteeples of the parifli churches of 

 St. Anne Soho *, St. Giles, and St. Martin, laid down by their 

 difference of latitude and departure from St. Paul's church, 

 obtained from the bearings and diftances in General Roy's Sur- 

 vey's in the Philofophical Tranfaaions, or the Account of Oper- 

 ations carried on for acco7npliJJnng a Trigonometrical Survej/ of 

 England and Wales, S^c. puhlijlied in quarto by Captain Mudge. 

 and Mr, James Dalhy. London, 1799, with 22 plates. 



The table is at pages 194, 195 of the laft mentioned work. 

 Whence and by obfervation with Hadley's Sextant, the da^ta 

 are : From St. Paul's 



St. Anne's bears S. 86°. 9'. 59'' W. 7754 feet.— Southing 

 518.4— Wefting 7736.6 feet. 



St. Martin's S. 74°. 23'. 59'' W. 6748 feet.— Southing 

 1805.2.— Wefting 6502.1 feet. 



St. Giles S. 94°. 36' 28" W. 6917 feet.— Northing 55,6-- 

 Wefting 6894.7 feet. 



• The fteeple of St. Anne's church has been fince rebuilt, and 

 ftands in the fame latitude, but nine inehes farther to the Eaft thau 

 before » 



B 2 Angle 



