of a simple Rain Gage. 9l^B 



be either slightly convex or concave, that is, to be either heaped 

 or not completely full. But, as the eye cannot decide when a 

 cubic measure is completely filled with water, and not heaped, 

 Mr Adam constructed two level triers,./; g, one for each of the 

 measures, A, and B, capable of detecting a deviation from an 



exact fill of either measure by a single drop from a fine tube, or 

 by less than the thousandth part of an inch. This was effected 

 by bringing the flat and sharp supports, ^, i, and the fine points 

 of the screws, A;, Z, of the level trier yj for example, exactly into 

 the same plane, upon a piece of plate glass, before it was placed 

 on the mouth of the cubic measure A. That measure being 

 placed on the table a b, and nearly filled with water, was then 

 accurately levelled by turning one or more of the screws c, d, e, of 

 the table, until the distances between the fine points of the screws 

 JCj Z, of the level-triery,* and their reflected images, m, n, seen in 

 the water, appeared to be perfectly equal when the leveUtrier was 

 placed successively in different directions upon the mouth of the 

 measure. The measure was then filled up by means of a small 

 glass dropping tube, until the fine points of the screws k, I, and 

 their reflected images m, n, came exactly into contact. This was 

 done with such precision, that less than a single drop too much, 

 or too little, was easily detected in either of the measures, espe- 

 cially in the smaller measure B. When the measures A and B 



