r 



► 





, F 



Sect. IX.] 



METEOROLOGY 



r\ <-^ f^ 



2^0 



leave a blank column for the " hygroraetric depression," 



must be 



in calculating which subsequently the zeros 

 applied. The reduction of the observations to derive the 

 elastic force of vapour at the dew-point is effected by the 

 formulae of Dr. Apjohn : 



F=/ 



d 



h 



88 ' 30 



. . (a); F=/ 



d 



h 



96 30 



• • f 



(h) 



(a) 



(^>) 



In these d is the hy- 

 )f the barometer, / the 



elastic force of vapour for the temperature shown by the 

 wet thermometer, to be taken from Table III, Appendix 

 and F the elastic force of vapour at the dew-point 



hich 



( 



other quantities being 



) 



formuls8 



enable us to calculate. With F so calculated enter the 

 same table under the column of Force of Vapour, and 

 the corresponding temperature is the dew-point, which, 

 however, is not wanted to be known but as a matter of 



curiosity. 



The Rain-Gauqe.—Thh may be of very simple con- 

 struction. A cubical box of tin or zinc, exactly ten inches 

 by the side, open above, receives at an inch below its edge 

 a square funnel, sloping to a sm,all central liole. On one of 

 the lateral edges of the box, close to the top of the cavity, 

 is soldered a short pipe, in which a cork is looseli/ fitted : 

 the whole should be well painted. The water which enters 

 the reservoir through the funnel hole is poured through 

 the short tube into a cylindrical glass vessel, graduated 

 to cubic inches and fifths of cubic inches. Hence, one 

 inch in depth of rain in the gauge will be measured by 



B^ 



^ J-r 



T: 



p- 



V 



