pe28any 
XVIII. 
A FRACTIONATING RAIN-GAUGE. By J. JOLY, D.Sc.,F.R.8., 
Hon. Sec., Royal Dublin Society. 
[Read January 17; Received for Publication, January 19; 
Published Marcu 8, 1900. ] 
In the course of a recent communication to this Society on the 
Geological Age of the Earth, I referred to the amount of sodium 
chloride carried in the atmosphere from the sea to the land as an 
important factor in the mode of estimating geological time, which 
I was then advocating. 
But little appears to be known on the matter beyond the broad 
fact that, in inland regions, the amount of this constituent in rain- 
water becomes very small. ‘There is also evidence, derived from 
observations made at different altitudes in Switzerland, that falling 
rain grows richer in this constituent as it descends through the 
atmosphere. 
This latter observation also leads to the inference that samples 
of rain collected at the beginning and during the progress of a 
shower should reveal a diminution in the quantity of sodium 
chloride. Bunsen has shown that certain dissolved constituents in 
rain- water diminish in this manner. 
The matter is well worthy of observation by those who live 
outside the impure atmosphere of acity. The chemical operation 
of determining the amount of chlorides present is a simple one. 
Continuous records should be made, and should include successive 
analyses of successive samples as referred to above, and simultaneous 
observations of wind direction. 
In order to effect the subdivision of rain received in the gauge 
into fractional parts as the rainfall progresses, I have devised the 
apparatus described in this note. It may be inexpensively made, 
and includes no valves or machinery. It cannot deceive, and may 
be constructed throughout of material which will not contaminate 
