170 
Proceedings of the Poyal Society 
4. Proposed Method of ascertaining the Temperature of 
Falling Bain. By Thomas Stevenson, F.B.S.E., Civil 
Engineer. 
A friend informed me some time ago that the late Principal J. 
D. Forbes had often noticed that a long continuance of rain 
resulted in a track of cold weather. Principal Forbes attributed 
this fact to the rain having a lower temperature than the atmo- 
sphere through which it fell. It does not appear, however, that he 
made any observations to determine the truth of his hypothesis, and 
as the subject is of considerable importance in other meteorological 
questions, it occurred to me that a simple instrument could be 
made for ascertaining the temperature of falling rain. This in- 
strument, a rough model of the funnel of which 'was lately shown 
at a meeting of the Scottish Meteorological Society, is repre- 
sented in the accompanying diagram, in which A B C is a 
conical funnel of thin glass, terminating in a small tube deep 
enough to contain the bulb of a thermo- 
meter, and recurved so as to form an off-let 
or waster. ADDA represents a box 
of wood into which the glass funnel is 
inserted, the space between the glass and 
the wood being carefully filled with saw- 
dust or any other had conductor of heat. 
The rim of the funnel should be bent over 
the upper edges of the box, so as to prevent 
the possibility of rain lodging itself among 
the sawdust.* The rain-drops intercepted by the funnel will pass 
off through the bottom of the box by the tube 0. 
By this or some such simple arrangement the temperature of any 
heavy fall of rain may be ascertained with tolerable accuracy. It 
is, of course, necessary that a dry bulb thermometer, properly pro- 
tected by a louvre boarded box, should be observed simultaneously 
with the rain thermometer. 
The difference of temperature between the air and rain could 
* It may be found better to carry the tube, at the second curve, horizontally 
through the side of the box instead of downwards. 
