The triangular quadrant, or, The quadrant on a sector being a general instrument for land or sea observations : performing all the uses of the ordinary sea instruments, as Davis quadrant, forestaff, crosstaff, bow, with more ease, profitableness, and conveniency, and as much exactness as any or all of them : moreover, it may be made a particular and a general quadrant for all latitudes, and have the sector lines also : to which is added a rectifying table to find the suns true declination to a minute or two, any day or hour of the 4 years : whereby to find the latitude of a place by meridian, or any two other altitudes of the sun or stars / first thus contrived and made by John Brown ...

X. To find a latitude at Sea by forward me∣ridian Observation or Altitude.

Set the moving object Sight to the Suns declination, shewed by the day of the Month, and rectifying Table, and skrew the turning sight to the leg center, and the Horizon sight to the moveable leg, or the

outside of the Crosse piece, according as the Sun is high or low (but note all for∣ward observations respecting the Horizon, ought to be under 45 degrees high, for if it be more it is very uncertain, by any Instrument whatsoever, except you have a Plummet and then the Horizon is uselesse) then observe just as you do in a forward ob∣servation, moving the Horizon sight till you see the Sun through the Horizon sight, and the Horizon through the object sight, or the contrary. (moving not that sight that is set to the day of the Month or Decli∣nation,) then whatsoever the moving sight shall shew, if you add 30 to it, it shall be the latitude of the place required; obser∣ving the difference in North and South Latitudes; that is, setting the sight to the proper declination, either like, or unlike, to the latitude-

Example. Suppose on the 10. of March when the Suns declination is 0—10. North, as in the first year after leap year it will be, set the stroke in the middle of the moving object sight to 10 of North Declination, and the Horizon sight on the moveable leg, then move it higher or lower, till you see the Horizon through one, and the Sun through the other, then the degrees be∣tween, is the Suns meridian altitude, if it be at Noon, as suppose it stayed at 21 30▪ then by counting the degrees between,

you shall find them come to 38. 40. then if you add 30. to 21. 30. it makes 51. 30. the Latitude required, for if you do take 0 10′ minutes from 38. 40. there remains 38. 30. the complement of the Latitude. Note, that this way you may take a forward obser∣vation, and so save the removing of the ••urning sight.

Note also, That when the Horizon sight shall stay about the corner, you may move the object sight 10. or 20. degrees towards the head, and then you must add but 20. or 10 degrees to what the sight stayed at; or if you shall set the sight the other way 10 or 20. degr. then you must add more then 30 so much. As suppose in this last observa∣tion, it had been the latitude of 45 or 50 degrees, then you shall find the sight to play so neer the corner, that it will prove inconvenient, then suppose instead of 0 10. I set it to 20 degrees 10′ North declina∣tion, which is 20. degrees added to the declination, then the Suns height being the same as before, the sight will stay at 41. 30. to which if you add 10 degrees, it doth make 51. 30. as before; here you must add but 10 degrees, because you increased the declination 20. degrees; but note by the same reason, had you set it to 19. 50. South declination, then it had been dimi∣nished 20 degrees, and then instead of 30 you must add 50▪ to 1 - 30. the place where

the sight would have stayed. Thus you see you may very neatly avoid this inconveni∣ence, and set the sights to proper and steady observations, at all times of obser∣vation.