66'8 The Account of a 



carried backwards and forwards in the mail coaches. If this 

 excellent scheme were executed, and the watches employed 

 equal to the best now made, it is probable that the true diffe- 

 rence of longitude would shortly be determined. The geodetical 

 situation of St. David's Head will, ere long, be ascertained from 

 a prosecution of the survey : a knowledge, therefore, of its true 

 longitude would be attended with eminent advantages. 



Lizard Light- Houses. 



The light-houses on this head-land were observed from Per- 

 tinney and Karnbonellis. At the latter, Pertinney bears 74 

 22' 41" south-west, from the parallel to the meridian of St. 

 Agnes ; and, as the angle between the western light-house and 

 Pertinney is 78 40' 5", it follows, that the bearing of the light- 

 house from the said parallel is 4 17' 24" south-east. Computing 

 with this angle and the distance from Karnbonellis to the light- 

 house, we get 3344 feet, and 126499 feet, for the distances of 

 that object from the meridian and perpendicular of St. Agnes : 

 therefore, admitting the length of the degree in the meridian, in 

 the middle point between St. Agnes and, the light-house, to be 

 60850 fathoms, and 61 182 for the length of a degree of a great 

 circle perpendicular to it, we get 20' 47",4, and 32",8, for the 

 small arcs which those spaces respectively subtend. These 

 data, with the latitude and longitude of St. Agnes, 50 18' 

 27", and 5 n' 55", 7, give the latitude of the light-house = 

 49 57' 44", and longitude west of Greenwich 5 n' 4",8, in 

 time, 20 m 44 s ,3. 



This light-house was also observed from the station on 

 Karnminnis. The triangle resulting from that observation, 

 together with the angle at Karnbonellis, is 



