THERMOMETRICAL OBSERVATIONS. 243 



Mean Latitude north . . 31 i 23.7 



From tlie refult of the above obfervations, the compafs line was too far 

 north by i' 2^".'I, or 518.55 perches, which dillance was carefully laid off 

 to the I'outh, and a ilone fet up at the termination, marked on the north 

 fide U. S. Lat. 7,1° 1799, — and on the fouth fide DOMINOS de 8. M C. 

 CAROLUS IV. Lat. 31" 1799- — From thii ilone, the line was corredled 

 back as in the foregoing cafe, agreeably to plate VIIL 



On our arrival at the end of the compafs line on the Mobile river, one 

 fcrious difficulty prefented itfelf, that was the continuation of the line 

 through the fwanip, which is at all times .^lmoft impenetrable ; but at that 

 feafon of the year abfolutely fo : being wholly inundated : — But fortunate- 

 ly we found in the neighbourhood of our camp a i'mall hill, the fummit of 

 which was juft elevated above the tops of the trees in the fwamp. From 

 the top of this hill, we could plainly difcover the pine trees on the high 

 land, on the eafl; fide. Upon afceitaining this faft, we fent a party- 

 through to the other llde, (along the water courfes, by which the fwamp 

 is interfecled in various dire(5lions), with orders to make a large fire in the 

 night with light-wood ; the fame was likewife to be done on the hill before 

 mentioned, to obtain nearly tlie diredion from one place to the other. — 

 The atmofphere was too mud) filled with fmoke, to difcern a flag, or other 

 fignal, — the woods being on fire on both fides ot the fwamp. — It happen- 

 ed unfortunately that the day before our fires were to be lighted, the fires 

 in the woods had extended over almoll the whole of the highlands, on both 

 fides of the fwamp ; by which fo many dead trees were fet on fire, that 

 there was no poflibility of difcriminating between them, and our fires. — It 

 was then agreed that the parties ihould light up, and e.xtinguilh their fires 

 a certain number of times ; making dated intervals. — This fucceeded fo 

 M'ell, that we became certain of not taking a wrong fire in determining the 

 angles. — Contrary to our expeiflation, a heavy rain fell on the fame night, 

 a Ihort time after we had finiflicd the eiiperiment, and extinguiflisd all the 

 fires in the woods. — The ftorm cleared off with a ftrong north-weft wind, 

 vdiich caiiied off all the fmoke, and enabled us to determine the angles in 

 the day, by eredl'ng fignals, which was accompliihed on the fecond day 

 of April. — This work v.ms connected with the obfervatory in the following 

 manner. At the obfervatory A (fee Fig. G, plate IX.) a meridional line was 

 traced, by taking the greateft elongations of « Urfas Minoris, both eaft, and 

 weft, with the tranfit and equal altitude inftrument : — equal diftances were 

 carefully meafured in each dircftion, and a fine mark placed at the termi- 

 nation of each meafurement, — the diftance between thofe marks was accu- 

 rately bifefled, and a fine mark placed at the point of bifeftion for the 



meridian. 



