of a simple Rain Gage. 287 



is closely applied a graduated brass scale * A', ri vetted to a strip 

 of mahogany, and, with the glass tube, supported by the appen- 

 dagesy'c i and / k. The appendages m I, and n o, have counter- 



sinked holes drilled in them aim, and 



w, by which the rain gage may be 

 screwed to a post in the place select- 

 ed for its use. The funnel mouth of 

 the brass cap AB a terminates on 

 the inside at the depth of 65 th inches 

 by an aperture p, about Jth of an 

 inch in diameter, through which the 

 rain entering at AB descends into 

 the tube b d, and rises in the glass 

 tube ch; at h the glass tube is co- 

 vered with a brass cap about 1 inch 

 in length, through the top of which 

 is drilled a hole about ^'^th of an 

 inch in diameter, to permit the escape 

 of the inclosed air when the water 

 ascends in it, and, like the small 

 aperture at p, to retard by its smalU 

 ness the escape of the water by eva- 

 poration, until it has been observed 

 and noted in the register ; after 

 which it is permitted to escape by 

 turning the stop-cock at e. 



Now, the lengths of cylinders of 

 unequal diameters, which contain 

 equal quantities of rain, being in- 

 versely as the areas of their bases, 

 or of sections parallel to them, in 

 order to find the length of a divi- 

 sion on the scale i k, which shall indicate a depth of 1 inch of 

 rain fallen around the rain gage, it is necessary to calculate 

 the area of the circular mouth AB, and also those of parallel 

 sections of the tubes bd, ch; then, dividing the former by the 

 sum of the latter, the quotient will indicate the length of the re- 

 quired division for 1 inch, by the repetition and subdivision of 



