4 
412 On the Method of determining the Time, Error, 
the results commonly obtained by it, are less correct than those 
obtained by General B., I apprehend the true reason is, that such 
minute accuracy is seldom thought necessary. 
General B.’s observations, however, will show what the instru- 
ment is capable of, and the friends of practical science are obliged 
by their publication. One obvious consequence deducible from 
them is, that the rate of a chronometer may be determined in a 
shorter time by this method than by meridian transits, or any 
other method that is practised. ‘The time deduced from a well 
observed transit of the sun, or a star whose place is well ascer- 
tained, may indeed be depended on as probably nearer the truth 
than that determined from a single altitude, however carefully 
taken; but the error determined from a single transit (of a star 
at any rate) is by no means of equal authority with a mean of the 
errors deduced from 10 or 12 altitudes of the sun. A compari- 
son of General B.’s results with the errors of the astronomical 
clock as determited by transits in the Greenwich observations 
will show this clearly enough. Besides, opportunities for obsery- 
ing the transits of proper stars are few compared with those for 
taking sets of altitudes, and a transit of the sun can be observed 
but once a day. 
In the method of regulating a chronometer by equal altitudes 
it is not necessary that the latitude should be known to any very 
great degree of exactness; but to practise the method of single 
altitudes successfully, it must be known with considerable accu- 
racy; and as a supplement to his paper, General B. promises to 
transmit another on the method of determining the latitude by 
a series of altitudes taken with a sextant near noon. 
As his method of findmg the time is so similar to mine, I think 
it prebable that the method of finding the latitude which he en- 
gages to communicate may also be in principle the same as that 
which I have practised for a considerable time; and my chief 
veason for wishing you to insert this letter in your respectable 
publication is, that our methods may be compared when his pa- 
per appears. 
{ shall expiain my method perhaps as well as I can in any 
other way, by giving you an account of some observations which 
1 made last autumn, for determining the latitude of this place. 
But before I enter on this account, I must inform you that the 
Trinty-House School is situated in the lower part of Newcastle, 
not far from the river; the steep banks of which are covered with 
houses; and that from the direction of the wind, and other cir- 
cumstances, the smoke, though at all times considerable, is some- 
times much more dense than at other times; and that the effect 
of this difference in the density of the smoke upon the refraction 
I am 
