REPORT OF THE RAIN GAUGES. 193 
rain, which it generally does, its course would be 
deflected by impinging on the sloping roof, and an 
upward current would be created, which, passing 
with increased rapidity over the ridging of the 
house, would carry the falling drops away, and 
prevent their being deposited within the area of 
the gauge. 
The inference from these considerations, 
coupled with the greater fall of rain, shown by 
other gauges placed upon the ground in similar 
districts, evidently was, that the returns would be 
under the truth. 
The committee, therefore, determined upon 
placing gauges in the ground as near as possible 
to the others, so as to be free from the influence 
of local currents, or other causes of interference. 
The gauge selected was the one now most ap- 
proved of and most commonly used, consisting 
of a hollow cylinder of copper or other metal, 
about seven or eight inches in diameter, and 
thirty-six or forty inches in length, with a receiv- 
ing funnel of the same diameter as the cylinder, 
and closely fitted to the top. Within the cylinder, 
a float rises, as it becomes filled with water. It 
is just so much smaller in diameter as to rise 
freely, and in the centre is fixed an upright rod, 
