VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. 243 



west of Cornwall. Whence it is inferred, that the distance from the Day-Mark to 

 Karnminnis, as obtained from the 309th triangle, is 190985 feet, and by the 310th, 

 1 90989 feet, which differs only 4 feet from the former ; and by the 3 1 Oth and 

 311th triangles, the difference of the distances from the same object, to the station 

 on Pertinney, is 17 feet ; which, allowing for the shortness of the bases, must be 

 considered as trifling. We may presume therefore, that had not the Day-Mark 

 been seen from Karnminnis, but from Sennen and Pertinney only, the observations 

 from which the angles of the 311th triangle are derived, would have afforded the 

 means of computing the distance with sufficient precision. In like manner the 

 312th and 313th triangles seem to prove, that the observations made to St. Agnes' 

 Light-house were sufficiently accurate, as there is a difference only of lb" feet be- 

 tween the distances of the Light-house from Pertinney. The ball on the top of the 

 Light-house was the object always observed ; and the Day-Mark being pyramidical, 

 we had the means of making the observations at the different stations to the same 

 point of this building. 



Of the distances of the objects in the Scilly Isles, intersected from the stations 

 in the west of Cornwall, from Sennen steeple ; the stone near the Land's End ; 

 and the Longship's Light-house. It is here observed, that as the observations 

 made to the Day-Mark, and St. Agnes' Light-house, may be supposed sufficiently 

 accurate ; and the ball on the top of the Longship's Light-house was also observed 

 under favourable circumstances, it will be proper to apply the corrections to the 

 horizontal angles, in order to obtain those formed by the chords. Taking, there- 

 fore, Pertinney as the angular point, and computing with the following data, viz. 



{Day-Mark . 4 = 154551 ") 

 St. Agnes' Light-house.. = 182207 > Feet. And 

 Longship's Light-house.. = 27883 J 



the angle at Pertinney, augmented for calculation, r the Day- Mark = 12° 17' 30" ) We get the 



between the Longship's Light-house and \ St. Agnes' Light-house = 6 15 25 J distance of 



ft. tag**. Light-house tan .... {g^^^tai- {2$gZ§!tf** 



Calculating also, with the distances of the two other objects in the Scilly Isles 

 and likewise those of Sennen steeple, and the stone near the Land's End from 

 Pertinney, with the included angles at the same station, we get 



Feet. Miles. 



f Day-Mark = 139521 = 26.4,3 



Sennen steeple from }"£■ A S n J s / Light-We = l6&25 5 = 31>40 



r j Flagstaff in St. Mary s = 157912 = 29.05 



(. Windmill in St. Mary's = 155299 = 29.41 

 f Day-Mark = 135343 = 25.63 



Stone near the Land's End from } £• A S"5 S ' L j? h £; ho ^ e = l6210 ° = 30.7 



J Flagstaff in St. Mary s = 153744 = 29.ll 



(.Windmill in St. Mary's == 151138 = 28.6'3 



Of the Scilly Isles, Menawthen is the nearest to the Land's End, being about 

 l^rV miles eastward of the Day-Mark ; and the cluster of rocks, called the Bishoj. 

 and his Clerks, the most remote, being 3f miles west of St. Agnes' Light-house. 

 Combining therefore the above particulars with those distances, we may conclude, 



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