of a simple Rain Gage. 283 



and ten-thousandth parts of an inch deep of rain. If the inside 

 diameter of the cylindrical glass measure K L be only half an inch, 

 the circular area of a section of it, viz. (i) ^x .7854 = .19635, or 

 nearly Jth of a square inch, will be contained 509 times in 100 

 square inches, the area of the square mouth of the filler. And 

 as the depths of square and cylindrical measures of equal ca^ 

 pacity are inversely as the areas of their bases, it is clear, that 

 to measure 100 cubic inches of rain water, which may be con- 

 tained in one inch deep of a square mouthed measure, Avhose 

 side is 10 inches, there will be required a depth or length of 509 

 inches of the cylindrical glass measure, whose diameter is only 

 half an inch. Consequently the hundredth part of this length, 

 or 5 inches and nearly ^\th of an inch of it, will be required to 

 contain 1 cubic inch, or to measure the hundredth part of an 

 inch deep of rain. Half an inch of it will be required to contain 

 ^^^th of a cubic inch, or to measure the thousandth part of an 

 inch deep of rain ; and consequently the ^^^th part of ^ inch, or 

 ^\th of an inch of this measure, will be required to contain the 

 hundredth part of a cubic inch, or to measure the ten-thousandth 

 part of 1 inch deep of rain. If a similar measure, f ds or |ths 

 of an inch in diameter, be graduated in the same manner, the di- 

 visions, even when carried only to tenths or to twentieths of a 

 cubic inch, are sufficient to enable a careful observer to determine 

 the depth of rain fallen around the gage to the ten-thousandth 

 part of an inch. Because by inspection, he can easily j udge of the 

 tenth or the fifih part of the smallest division on the scale ; which 

 tenth or fifth, being about ^^^th of an inch in length, indicates 

 the ^i^jdth part of a cubic inch, or the ten-thousandth part of 

 a depth of 1 inch of rain. Here it is obvious that the metallic 

 filler, and the graduated cylindrical glass measure, are the prin- 

 cipal parts of this rain gage ; that its value depends on the ac- 

 curacy with which these parts are constructed ; and that it may 

 be very accurately made at half the expense of the common and 

 patent rain gages, which show the depth of rain falling around 

 them only to the hundredth part of an inch. 



The rain gage above described, has been in use since the 

 18th of September 1829, and appears to Mr Adam to answer 

 its purpose well. For, though the inside diameter of the larg- 

 est graduated measure used is nearly Jths of au inch, the dis- 



