564 PHILOSOPHICAL TRANSACTIONS. [aNNO 1758. 



could not meet with any ancient noted city of Africa, that had a mint erected in 

 it, and a name beginning with the letters this piece exhibits ; he could not attri- 

 bute it to any town in that part of the world. He rather thinks it might have 

 belonged to Agrigentum, an ancient city of Sicily, where money was coined, 

 when that part of the island which appertained to the Carthaginians, was in 

 alliance with that people, or had some commercial connections with them. 



•i'ibjio'j tAdthu^i lioii 

 XLI. Introduction to the following Observations, made by Messrs. Charles 



Mason and Jeremiah Dixon, for determining the Length of a Degree of Lati- 

 tude, in the Provinces of Maryland and Pennsylvania, in North u4merica. 

 By the Rev. N. Maskelyne, B. D., F. R. S., p. 27,0. ;,^ ^mr.!. 



Messrs. Mason and Dixon, who observed the last transit of Venus over the 

 sun at the Cape of Good Hope, under the direction of the r. s., had been since 

 engaged, by Lord Baltimore and Mr. Penn, to settle the limits between the 

 rovinces of Maryland and Pennsylvania, in North America ; which they per- 

 formed partly by trigonometrical, and partly by astronomical observations. In 

 the course of this work, they traced out and measured some lines lying in and 

 near the meridian, and extended, in all, somewhat more than lOO miles; and, 

 for this purpose, the country in these parts being all over-grown with trees, large 

 openings were cut through the woods, in the direction of the lines, which formed 

 the straightest and most regular, as well as extensive vistos that, perhaps, ever 

 were made. 



They perceived that a most inviting opportunity was here given for determin- 

 ing the length of a degree of latitude, from the measure of near a degree and 

 half. And, one remarkable circumstance very much favoured the undertaking, 

 which was, that the country through which the lines run, was, for the most 

 part, as level as if it had been laid out by art. 



The astronomical observations had been taken with an excellent sector of 6 

 foot radius, constructed by Mr. Bird, the first that ever had the plumb-line 

 passing over and bisecting a point at the centre of the instrument. This instru- 

 ment was so exact, that they found they could trace out a parallel of latitude by 

 it, without erring above 15 or 20 yards; in doing which, it should be observed, 

 that they generally used the same stars, commonly 6 or 8 or 10 in number, at 

 the several stations, and made a double set of observations at each station, with 

 the limb of the sector turned both to the east and to the west. This sector had 

 been set up at the northernmost point of the lines before-mentioned as proper 

 for determining the length of a degree of latitude. In order to determine the 

 difference of latitude between this point and the southernmost point of the lines, 

 or the amplitude of an arch of a meridian contained between their parallels, it 

 was necessary that the sector should be also set up at the southernmost point. 



