VOL. XXXVIII.] PHILOSOPHICAL TRANSACTIONS. 673 



solar vane should not be less, but rather larger, than a silver shilling, with its 

 vertex most exactly set. And that the utmost care be taken to place the mid- 

 dle of the curve at the centre exactly perpendicular to the line or radius of 45 

 degrees. As the observer must also take care that the two vanes on the limb 

 be kept nearly equidistant from that degree ; and it may be best to give the 

 horizontal vane only one aperture. 



Note, That the radius of the quadrant being divided into 20 equal parts, the 

 centre X, in fig. 12, of the curvature of the horizon-vane ab, must be 12-iV 

 of those parts from the centre c of the quadrant. The breadth, ab or gh, of that 

 vane, should be -^V of the whole radius, that is, -jL- on each side of the centre c. 



The Description and Use of an Instrument for taking the Latitude of a Place 

 at any Time of the Day. By Mr. Rich. Graham, F. R. S. N° 435, p. 450. 



The necessity of finding the latitude a ship is in, is too well known to be in- 

 sisted on : frequent opportunities of observing the latitude must consequently 

 be of very great advantage to navigation. The method usually practised, is by 

 taking the sun or stars meridian altitude or zenith distance : in this case, if the 

 sun does not shine but for some small time only, before noon and after, though 

 it be clear all the rest of the day, it is of no use for this purpose. In J 728, 

 Mr. Fatio proposed a method for finding the latitude, from two or more obser- 

 vations of the sun or stars, at any time, the distance of the said observations, 

 in time, being given by a watch ; but as his method requires a vast number of 

 computations, and a good skill in spherical trigonometry, it has very seldom 

 been made use of, and never but by good mathematicians. The instrument 

 here described will answer the same end, and has these advantages : 1st. It may 

 be easily understood by seamen. 2dly, It immediately shows the latitude of the 

 place. 3dly, It gives the time of day at sea, when no other instrument can. 

 4thly, It may be made as large, and consequently as accurate, as is desired. 



A Description of the Instrument is as follows. — abc, fig. 4, pi. 17, repre- 

 sents part of the hemisphere of a large globe (half the globe, and the part be- 

 low the tropic are cut off, that it may take up the less room.) ac, half the 

 equator, divided into 12 hours above, and 180 degrees below, and subdivided 

 into minutes, as is likewise the lower tropic dd ; ee a moveable graduated 

 meridian, turning on the axis ff ; a an index to fix it to any hour, by the 

 means of the screw h. lil a circular beam-compass, tiie centre li to be fixed 

 on the meridian to any degree and minute of declination, by the method com- 

 monly called Nonius's divisions : k the point for drawing arches, which is like- 

 wise fixed to any degree and minute by the same method. As the meridian is 

 at some distance from the globe, l is a piece of brass to fix on the meridian, 

 marked with Nonius's divisions, with a point reaching down to the intersection 



VOL. VII. 4 R 



