676 PHILOSOPHICAL TRANSACTIONS. [anNO 176Q. 



of the stones on Fenwick's Isle be supposed truly given, in the former account, 

 5' 45* of a degree, then the difference of longitude of Lewestown and the point 

 A will come out about 1' of a degree, or 4* of time less; for Mr. Dixon says, 

 that the distance of the stone on Fenwick's Isle, east of the point a, is 35 Eng- 

 lish miles wanting tOO yards. Now this is equal to 30' 26* of a great circle 

 = 38' 51" of longitude; from which subtracting 3' 45", there remain 33' 6" for 

 difference of longitude of Lewestown and point a = 2™ 12-^' of time, or S-J-* 

 less than found before; and this latter I take to be nearest the truth. If this 

 be so, Lewestown is very nearly under the same meridian with the southernmost 

 part of the city of Philadelphia, or more accurately 13" of longitude, answering 

 to 1^ of time, east of it. For, by Messrs. Mason's and Dixon's measure of a 

 degree, the point n, in their survey, is 2' 19" of longitude west of the point a; 

 and N, by measurement, is 3 1 English miles due west of the southernmost part 

 of the city of Philadelphia, answering to 35' 12" of longitude; from which sub- 

 tracting 2' 19", there remain 32' 53", answering to 2'" 1 1^' of time, for the 

 difference of longitude of the southernmost part of Philadelphia, east of the 

 point a. But Lewestown is found above to be 33' 6" of longitude = 2™ 124-* 

 east of the jraint a, and consequently is 13" of longitude, or about P of time 

 east of the southernmost part of the city of Philadelphia. Nevil Maskelyne. 



LX. Observations of the Transit of Fenus over the Sun, made at the Round 

 Tower in IVindsor Castle, June S, 1769. By Daniel Harris, Master of the 

 Royal Mathematical School in ChrisCs Hospital, and F. R. S. p. 422. 

 The latitude of St. Paul's, or, which is the same thing, of the Royal Mathe- 

 matical School in Christ's Hospital, by the mean of a great number of observa- 

 tions, Mr, H. makes to be 51° 30^' n. and by a mean of several double altitudes 

 of the sun, taken in a saucer of treacle and water, screened from the wind, he 

 finds the latitude of Windsor Castle to be 51" 28+' n. the difference of latitude 

 therefore between those two places is 2^ geographical miles; with which, and 

 the bearing of St. Paul's from the castle n. 82° 30' e. variation 20i degrees 

 allowed for, he makes the difference of longitude between tliem (by Mercator) 

 to be 304- miles, which is equal to 2™ 2* of time. The.-efore, with tiie distance 

 of 22 miles, between Windsor and St. Paul's, equal to IQ geographical ones, 

 and the difference of latitude, by observation, between the two places 2-^ miles, 

 Mr. H. finds the departure to be 18.8 miles, which gives 30.2 miles of longi- 

 tude, equal to 2"* P of time, agreeing within a second to the former method. 



The difference of longitude, or difference of meridians, therefore, between 

 the round tower Windsor castle, and St. Paul's, London, Mr. H. ventures to 

 put at 304^ miles, or 2™ 2' of time, though he is persuaded, if any thing, it is 

 rather more than less; to which if we add the difference of longitude in time 



