r 274 ] 
XL II. Obfervations for determining the 
Length of a Degree of Latitude hi the 
Provinces of Maryland and Pennfylvania, 
in North America, by Meffeurs Charles 
Mafon and Jeremiah Dixon. 
Read Nov. 24, T N this work, the flrffc thing to be con- 
fidered was, how to continue a right 
Jine : and this was done by betting up marks with the 
aftiltance of an equal altitude or tranfit inftrument (for 
it was contrived fo as to ferve either purpofe at pleafure), 
made by Mr. John Bird, of the fame conftruCtion with 
that defcribed by M. Le Monnier, in the preface to the 
fingle volume of the French Hiftoire Celefte. 
The cylindrical ends of the crofs axis of the te- 
lefcope were laid in two angles of the fupporters, 
which rofe perpendicularly from a horizontal bar, 
that was fattened firmly to the upper part of the ver- 
tical axis. The axis of the telefcope was fet truly 
horizontal, by a fpirit level hung on its cylindrical 
ends. 
The brafs frame, which receives the vertical axis, 
was fcrewed to a poft fixed in the ground, in the di- 
rection of the line which was to be continued. 
When the vertical wire in the telefcope was 
brought to bifeCt any mark, it was kept in that di- 
rection, by confining firmly, between two pufhing 
lcrews, a horizontal arm that projected from a collar 
that furrounded the vertical axis and, to prove that 
a l'mall fhock would not alter its pofition, a fmall 
7 prefllire 
