Description of an Improved Rain Gage. 331 



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

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

 hundred, 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 gage may 

 be made of tin, or sheet iron painted or japanned, but cop- 

 per is more durable. The area of the funnel, and that of 

 the top of the body part, are the only parts that need atten- 

 tion in the construction. These ought to be made tolerably 

 exact. A strong hoop should be fixed around them on the 

 outside to preserve their figure true. 



In every operation of weighing, the weight of the gage, 

 moistened in the inside, must be deducted from the gross 

 weight; the remainder is the corrected weight of the water 

 with which the tables must be entered. 



In the case of hail, snow, sleet, or frozen water, being in 

 the gage, it is not necessary to melt its contents into water, 

 as the changes effected by temperature and pressure 

 make no difference in the weight. 



The use of scales and weights may be dispensed with, by 

 substituting a steelyard, so constructed that the moveable 

 weight on its arm might indicate by its position, not the 

 weight, but the inches and decimal parts of its correspond- 

 ing altitude, without reference to the tables, and without 

 calculation. 



The advantages of this method of finding the quantity of 

 rain, in linear inches of altitude, will be appreciated by ad- 

 verting to the circumstanceof our having a tangible quantity, 

 as an unerring guide to that which is nearly imperceptible. 

 Twenty five grains and a half, a sensible q^uantity in a good 

 balance, pointing out the difficultly visible division of the 

 ToVa P^'"'^ of 30 inch. Suppose the problem reversed; 

 that the cubical contents of the water, or its weight, were 

 required, from the observed attitude. The chances of er- 

 ror would all be against the accuracy of such a determina- 

 tion. The difficulties of the task, independently of the 

 aforementioned causes of variation, would evidently be in- 

 surmountable. 



I had a gage constructed on this principle, twelve or 

 fourteen years ago, for my friend Dr. Akerly, who inform? 



