On the Deficiency of Rain in an elevated Rain-gauge, 421 

 a . tan (45° — - j, and the south pole is south of the central point 



oy a. tan (45°+ |j, or «.cotan(45°— |J. 



(5) Bisect the line joining the pole3 (the point of bisection will 

 be south of the central point by a . tan a), and through the bisect- 

 ing point draw an indefinite straight line at right angles to the 

 polar axis. (This line represents the parallel for south latitude 

 «.) On this transversal line will lie the centres of all the circles 

 representing meridians. 



(6) Let y be the angular measure of longitude east of the 



Point of Reference, of any meridian which is to be drawn. The 



eastern intersection, of the circle representing this meridian, with 



V 

 the transversal line, will be at the distance a . secant « . tan ~ 



from the polar axis ; and the western intersection will be at the 



distance a . secant a . cotan ^. The western distance of the centre 



of the circle will be a . secant « . cotan y, and the radius of the 

 circle will be a . secant a. . cosecant y. 



When, by means of these formulae, the circles for Parallels and 

 Meridians have been drawn, then concentric circles are to be 

 described having the centre of the map for their centre, and with 



10° 20° 



radii successively equal to a .tan— -, a. tan ---, &c, representing 



KJ til 



great-circle distances 10°, 20°, &c, from the Point of Reference; 

 and radii are to be drawn at equal azimuthal angles. Then the 

 map may be used for laying down the intersections of meridians 

 and parallels (as described in article 21) for any projection what- 

 ever, with the same Point of Reference. 

 Roval Observatory? Greenwich, 

 September 25, 1861. 



LIV. On the Deficiency of Rain in an elevated Rain-gauge, as 

 caused by Wind. By W. S. Jevons, B.A. of University Col- 

 lege, London*. 



[With a Plate.] 



1. ¥7>R0M the year 1767 many meteorologists have held the 

 Jl settled opinion that the larger part of the rain which 

 falls upon the surface of the earth does not proceed from the 

 clouds, as we should naturally suppose, but is derived from the 

 lower strata of the atmosphere, within 200 or 300 feet of the 



* Communicated by the Author, having been partly read at the meeting 

 of the British Association at Manchester, September 1SG1. 



