^86 Mr Adam's Description and Explanation 



were thus adjusted, and a tin-plate tube S, made exactly to fit, 

 and slide upon the cylindrical measure KL of the rain gage, 

 ip graduation from L to K was commenced by pouring into it 

 successive fills of the measure B, and graduating it, at each fill, 

 by means of a fine diamond pencil drawn across the tube KL, 

 along the upper edge of the sliding tube S, when placed exactly 

 at the surface of the water ; three longitudinal lines, at proper 

 distances, being previously drawn from L to K by means of a 

 longitudinal section, op, of a cylindrical tin-plate tube made 

 closely to fit, and slide upon it. The measure KL being thus 

 graduated, or divided, into portions having the capacity of 

 cubic inches and tenths of a cubic inch, the subdivisions were 

 afterwards drawn on the tube by dividing each tenth of a cubic 

 inch on large tubes into two, or on small ones into ten, equal 

 parts. This method of graduation, though tedious, has obvi- 

 ously the advantage of great accuracy, by being independent of 

 any inequalities which may exist in the bore of the tube, an ad- 

 vantage which was indispensable when it was proposed to deter- 

 mine the depth of rain fallen around the rain gage to the 

 ten- thousandth part of an inch. If the graduation of the glass 

 measures, professing to shew cubic inches and decimals of a cu- 

 bic inch, sold in the chemical apparatus shops in London at four 

 or five shillings each, could be depended on, the rain gage 

 above described might be procured at the expense of a few shil- 

 lings. But, as this is not the case, where much accuracy is 

 wanted, it is necessary to incur the higher expense, or the trou- 

 ble, of a careful graduation. 



The common rain gage, represented in the annexed dia- 

 gram A B c A, on a scale of |th of an inch to 1 inch, as made 

 and sold in Edinburgh at L. 4, 4s., has a funnel-mouthed brass 

 cap ABa about 7 inches in depth, of which the lower part a b 

 slides about 2 inches tightly over the upper extremity of a cy- 

 lindrical brass tube bd, 2-07 inches in inside diameter, and 30*5 

 inches in length. The lower extremity dg of this tube is fur- 

 nished on one side with a stop-cock d e, and on the other with a 

 strong brass canal appendagey*^ i, through which the rain water 

 descends and rises in the glass tube c h until its surface be at the 

 s ime level in both tubes. To one side of the glass tube ch, which 

 is -SSi' of an inch in inside diameter, and 30*5 inches in length, 



