338 Proceedings ef Philosophical Societies. {[May, 
object of Mr. Kerr’s plan is to ascertain what is the real area of the 
mouth, or ‘surface exposed during the shower, and so to find the 
true quantity impinged on a given surface. The instrument is also 
constructed to show the quarter from which the rain comes. To 
accomplish these ends, he employs two cups, which are so placed 
that the planes of their mouths make a right angle with each other. 
The mouth of the one is vertical, and the mouth of the other is 
horizontal. We have thus all the varieties which can happen be- 
tween 0° and 90°, or between a perpendicular fall of rain, and one 
that is blown parallel to the horizon. The cups are each of them 
connected with a tube, which conveys the water to the recipients 
below, and the whole is attached to a wind-vane, which turns round 
upon a strong iron rod, By this means the mouths of the cups are 
always kept in a proper pesition, fully exposed to the shower. The 
iron rod which supports the whole passes through a square hole in 
the middle of a cistern-frame divided into 16 spaces, and containing 
two concentric sets of cisterns. The inner cisterns receive the drops 
which fall from the tube connected with the vertical cup, and the 
outer cisterns receive the drops which fall from the tube connected 
with the horizontat cup. As the cisterns remain fixed, and the 
gage tubes move with the vane, it is evident that the water can only 
drop into that cistern which happens to be under the end of the 
tube at the time, so that we can easily tell what way the wind blew 
during the shower. ‘Thus if we find water in the south cistern, the 
vane above must have pointed in that direction. The quantity of 
water found in each cistern is afterwards poured into a graduated 
glass tube, and an account of the contents kept in a book having a 
column ruled for each cistern. 
In order to find the true surface exposed, it is necessary that we 
should have the angle at which the rain is impinged on the cups. 
This angle is found by comparing the whole quantity of water in the 
cisterns of the horizontal gage with the whole quantity of water in 
the vertical gage. ‘Thus suppose we find an equal quantity in each, 
then the rain must have fallen at the angle of 45°, for at that angle 
the cups present equal surfaces. But it we find more water in one 
set of cisterns than in the other, the rain must have fallen at a 
greater angle on that set which contains most; and the angle may 
be found by the help of a table constructed to show the obliquity 
which corresponds to any given inequality of water in the recipients, 
This rain-gage, in Mr. Kerr’s opinion, will not only be enter- 
taining to the meteorologist, but also useful to the farmer, who, by 
a series of observations, may be able to determine more accurately 
the climate of his farm.- It will point out to him what places re- 
quire to be most secured, when he is constructing places of shelter 
for cattle, hay, or corn-stacks, planting trees, and many other rural 
operations. 
At the meeting of Jan. 6, Dr. Macknight read a mineralogical 
description of Ravensheugh, on the west of East Lothian, It is 
Pe a ee eee ee — eel 
