112 Mr. Chilton on an improved Rain Gauge. [Aug. 



2. If the weight, reduced to grains, be found in Table 3, the 

 corresponding height will be found opposite to it in the adjoining 

 column ; but as, in this example, it is not, take the nearest, less, 

 number to it from the table, and subtract it from the weight of 

 the water, marking the corresponding height in inches, &c. 

 Enter the table a second time with the difference and take the 

 nearest less number to it, together with its correspondent height, 

 which subtract from the difference, and with the remainder enter 

 the table again, if necessary, thus, 



Corres- 



Weight of water pondent 



in grains. height. 



The nearest number in the table, less than 142406-25, 



which must be subtracted, is 126262*5 500 



Difference IGUtPld 



The next number in the table, less than the 



difference, is 15151-5 0-60 



which, when subtracted, leaves the re- 

 mainder 992-25 



The nearest number corresponding to the 



remainder in the table, is 1010-1 0-04 



The sum of the corresponding heights gives Inches 5-64 



It is obviously not necessary to be restricted to either the form 

 or the size of the above described gauge. If the cylindrical 

 form be thought to possess any advantages over that of a square 

 prism, it is easy to find the diameter of a circle whose area shall 

 be equal to 100 square inches, by the well-known rule, viz. d = 



a /— 4— , where d represents the diameter, a the area, and -7854 



the area of a circle, whose diameter is unity. If any other size 

 should be thought more convenient, as, for instance, one whose 

 area is only half of that of the above-described gauge, the same 

 rule, if cylindrical, will give the corresponding diameter, or if a 

 square-mouthed one be preferred, the side of the square is 

 obtained by extracting the square root of fifty. But it must be 

 remembered that whatever relation the area we pitch upon may 

 bear to 100 square inches, the same relation will subsist between 

 the final result, and that which is given by the tables : thus if the 

 area of the gauge be fifty square inches, as this is the half of 

 100, we must take half the sum of the tabular heights for the 

 true altitude. 



It is not necessary to be very particular in the choice of a 

 balance ; a pair of good common scales will answer, with true 

 weights, either troy or avoirdupois. The gauge may be made of 



