1840.] Fort William, and Futtehghur. 87 



but the difference of weight is not much, and after being ac- 

 customed to it, it feels steadier in the hand than the sextant. 

 It may indeed happen when a ship has much motion, that in 

 one position of the circle, the right hand being further from the 

 eye than it is with a sextant, a degree of inconvenience is felt, 

 but it is soon surmounted, and is moreover balanced by the 

 convenience of having two handles to the circle, so that the 

 face is never held downwards, as the sextant must frequently be. 



There is indeed a little longer time required to read off the 

 three verniers than the single one of the sextant, and this may 

 sometimes make the assisting observers of the sun and moon^s 

 altitude impatient, or less attentive. For my part, I think that 

 lunar observations are most satisfactorily taken without an assist- 

 ant, except one to note the watch, (and one may be dispensed 

 with) all that is required, is to have, say, a sextant and a good 

 quadrant. Then proceed to take one altitude of the moon, and 

 lay the sextant down ; — that done, take one of the sun, with 

 the quadrant, and lay it down ; — then take two or three sets 

 of distances with the circle on both arcs, and then observe the 

 altitudes of sun and moon, noting all the times. 



All these things, with a little pre-arrangement, may be soon 

 and calmly done, which is the chief thing, and readily reduced 

 to the mean of times and distances; but if two instruments 

 are not available, the altitudes may be taken with the circle. 

 On shore the altitudes of sun or star and moon may be taken 

 with a well adjusted theodolite, or sextant, or the circle, and 

 if the observer has not an assistant, the seconds of time may be 

 conveniently noted by the beat of a metronome, but a prac- 

 tised observer will himself count the seconds correctly. Or if the 

 latitude and time are correctly known, as they can be on land, 

 altitudes of the sun, moon, or stars, may be calculated. In in- 

 vestigating longitudes on shore, the time should always be 

 determined by equal altitudes of the sun or stars, which may be 

 taken by two or three sextants with the artificial horizon, or 

 by meridian passages of stars made with a portable transit 

 telescope. Lithographic forms are useful, in which to fill 

 up all the figures of calculations, and these should always be 

 preserved. 



