330 
Description of 
the collected water is received in its receptacle, also a cylinder 
of two inches diameter, the area of the surface exposed being 
five inches wide by ten in length, or fifty inches, corresponding 
with the horizontal rain-guage; on the back is soldered a tin 
tube, with an agate placed at top (to prevent friction); in this 
tube is inserted a pointed iron rod, on which the whole apparatus 
traverses, carrying with it the receptacle and its contents; and 
which, if it be properly mounted, will turn with the slightest 
breath of air. 
After each shower, the quantity of rain found in both the 
receivers must be accurately measured to hundredths of an inch, 
and be carefully noted; distinguishing that found in the horizon¬ 
tal pluviameter by the letter H, and the quantity found in the 
perpendicular one call P. 
Then the quantity H will be to P as the radius is to the tangent 
of the inclination of the rain from its perpendicular descent, or 
the angle of its drift. The real area positively exposed will be as 
the sine of the inclination (just found) is to the radius; or, as 
the radius is to the constant logarithm 1.69897, so is the sine of 
the rain’s inclination to the true area of the surface presented to 
the shower. 
Then as this area is to the quantity called H, so is the area 
fifty inches to the true quantity fallen, and which will indicate 
the same proportion whether the pluviameter be placed in an 
exposed or sheltered situation. 
It may be objected that even this somewhat elaborate method 
is not exact, because the oblique direction of the rain’s descent 
will cover a larger space, and consequently cause a smaller quan¬ 
tity to fall on a given spot; but, if we consider that the water 
must be intercepted by all objects, whether erect, raised, or in 
fact inclined in the smallest degree to the horizon, and by them 
be conducted to the earth, the proposed plan is, I consider, the 
best that has been adopted to ascertain the true quantity fallen : 
at all events, I would strongly recommend that a careful record 
be made of the rain collected in both the horizontal and perpen¬ 
dicular pluviameters, which should be placed as near to each 
other as may be ; this, if attentively watched, and the contents 
