212 ASTRONOMICAL and 



whicli fuppofe to be at S. The firft lantern was then removed and the 

 aperture brought.to coincide witli the point of biieclion. In the afternoon 

 of the fame day, the vertical fibre of the telefcope being brought to hifeifl 

 tlis aperture of the lantern at S, Arcturus was again obferved in its afcent, 

 and the morning follov\ing in its defcent. — The inftrument was reverfed as 

 in tlie firft cafe, and the aperture of the fecond lantern which was now put 

 on the flatted piece of timber V, placed about i S inches below the firft, 

 and brought truly into the direction of the vertical fibre by an affillantw — 

 The candle in the firft lantern at S was then lighted, and the flames of 

 both v.-ere biieifted by the vertical fibre. Being by this obfervution con- 

 vinced, that tlie telefcope moved accurately in the prime vertical, the line 

 was then opened weft with that diredion, the diftance of two hundred and 

 thirtv-five perches to high water mark : as the inftrument then defcribed the 

 prime vertical, the offset into tlie parallel of latitude, (which became a 

 tangent to the arc'*, was laid off to tlie north, being two and an half inches, 

 where a hewn poft was fet up and ftirrounded by a mound of earth. — At 

 S, the tangent of an angle of 2' 36" 45'" having BC for its bafe v. as laid 

 orF to the north by meafurlng from the middle of the aperture of the lan- 

 tem, the ciftance of 10.68 inches, at tlie termination which fuppofe to be 

 at r, a fine mark was placed, which the verticlc fibre was brought to bifecl. 

 — This mark gave the direftion of an arc, which continued the diftance of 

 ten miles, would again interfeift the parallel of latitude, which would then 

 become a chord to the arc, and the oitsets be to tlie fouth, and fall within 

 the vifta we were opening : by taking fo fmall an arc, the trouble and ex- 

 pence of opening two lines through one of the moft impenetrable coun- 

 tries in tlie world was avoided. 



of the firft mile! Ft 

 :aft of the tranfit > 1 



f 3 



At the termination of the firft mile! Ft. In. 

 which was 85 perches eaft of the tranfit > 1 o was laid off to the fouth. 

 ftation at B an offset of 



J 



On the lytli of July, we mowed our camp to Big Bayou Sara, about 

 37" north of the parallel of 31" and 9.6 perches eaft of the ten mile poft. 

 On die 1 9th fet up the clock, and prepared to obferve fuch of the eclipfes 

 of 1^ 's fatellites as ihould be vifible while we continued at that ftation. 



Aug. 



