i ~o Gen. Rot’s Account of 
t 
firing much more time than we could afford, confidently with 
the engagements entered into with the French Gentlemen, 
for the co-operation on the Coaft. At particular times, efpe- 
cially in hot weather, there was fuch a tremulous motion or 
boiling in the air, that it was only during a very fhort fpace, 
chiefly in the mornings and evenings, that the objects were 
fufficiently diftinfl to be obferved with accuracy. So difficult 
it is to do any thing perfectly good in this way, that a whole 
day has frequently been Ipent, after watching with anxious 
care, in obtaining a Angle one that was perfectly fafcisfadory ! 
At fuch times as thefe it would have been abfurd to have 
attempted to* change the zero, which always rendered it necef- 
fary to re-adjuft the inftrument by its levels. 
In very favourable circumftances of the weather a good- ob- 
iervation by day is preferable to one by the white lights at 
night ;- beeaufe, in the firft cafe, the obferver has time at his 
leifure nicely to bifeffb a fine flag-ftaff, and repeatedly to read 
off the angle ; whereas, in the fhort duration of the burning 
of the light, he is fomewhat hurried, from the fear of lofing 
fome of the lights at other diftant ftations, if two of them 
happened to come together, which now and then they did, 
from the irregularity of the rates of the watches of the artil- 
lery-men attending at the different ftations. It was, however, 
by the affiftance of the white lights only* that the moft diftant 
ftations could be rendered vifible ; and there cannot be a doubt 
that, in great trigonometrical operations, of this fort, they will 
be universally adopted hereafter. 
Sometimes an obfervation has been entirely loft, or at leaft 
that which had been obtained was not thought a very good 
one. In fuch cafes a blank has been left in the column: of 
obferved angles, and alfo in that exprefling the error. But no 
c bad 
