156 Scientific Proceedings, Royal Dublin Society. 
In Table 12 the water-temperatures 7 of the open cup, the 
differences 6 between the vapour-tensions at the temperatures of 
the water and dew-point,’ the velocity W of the wind at a height 
of 45 feet, the evaporation # in grains from the open cup, and 
the number of observations, have been arranged in groups 
corresponding to each 5 per cent. of relative humidity in the free 
air for the two periods 5to8 p.m. and 8toll p.m. According to this 
we see that, saving a few minor irregularities introduced when the 
number of observations in any group is too few—(1), the tempera- 
ture of the water is at a minimum when the air is about one-half 
saturated, but increases pretty uniformly on either side, as the air 
becomes drier or damper, to at least 25 per cent. on one side, 
and to about 80 per cent. on the other. Relative humidities, 
exceeding 80 per cent., are generally associated with rain, and 
hence the low temperature conditions. 
(2.) The velocity of the wind is apparently non-effective. 
(5.) The differences of vapour-tension decrease as the relative 
humidity increases ; and (4), so does the rate of evaporation. 
So far as (3) and (4) are concerned, therefore, there is nothing 
to show whether the decrease of evaporation is dependent upon 
the increase of relative humidity, or the decrease in the differences 
of vapour-tension. 
1 The wind is known to be most influential in promoting evaporation. The 
Kimberley observations, however, have not hitherto yielded sufficient information 
upon which to base a numerical estimate of its effect. The reason seems to be that a 
strong wind often brings an increase of moisture, and therefore its effect is almost 
entirely neutralized. 
