138 Scientific Proceedings, Royal Dublin Society. 
to reduce the scale-readings to depths in inches has been computed 
equal to 00415. This reduction, however, has not been performed 
in every case for the purposes of this paper. The instrument is 
suspended in a large louvered screen of 8 x 8 x 8 feet dimensions. 
2. A galvanised-iron tub of 14 inches diameter and 18 inches 
deep, having a tap at the bottom for the purpose of adjusting the 
water-surface quickly and accurately to zero. It stands alone in 
a single-louvered screen whose dimensions are 46 inches long, by 
34 wide, by 6 feet high over all. The amount of evaporation is 
read from a lever which, actuated by a float, travels over a 
graduated dial, and magnifies the fall in level ten times. A 
thermometer is attached in such a way that its bulb dips just 
beneath the surface of the water. 
3. A circular steel tank, rather over 46 inches diameter, and 
29 inches deep, placed in the centre of a cemented brick cistern of 
about 7 feet square. The walls of the cistern rise some 8 inches 
higher than the rim of the tank. ‘The outer cistern is kept supplied 
with water up to a level about equal to that of the evaporating 
surface of the tank, but there is not any communication from one to 
the other. An iron pipe opens under the centre of the tank, passes 
through the side of the tank—to which it is secured by water- 
tight check-nuts—outwards through the wall of the cistern, and 
thence underground to a vertical cylindrical vessel set under the 
floor of the barometer room. A large, hollow copper ball floating 
in the cylinder carries a vertical wooden rod which is attached to 
the short end of a light brass lever balanced upon knife-edges. A 
pen at the other end of the lever writes a magnified record of the 
fluctuations in the level of the water upon a long drum rotated by 
clockwork. Thus the records obtained are of both evaporation 
and rainfall, the pen rising for the one and falling for the other. 
4, A piece of apparatus intended to give the evaporation 
from the surface of water in vessels placed at the bottom of 
heavy metal tubes of 3:13 inches diameter, and 1, 2, and 3 feet 
long, respectively. ‘The tubes are furnished with broad flanges for 
feet, and stand when in action upon a sheet of thick rubber 
insertion nailed to a block of wood. They are also furnished 
with swing-handles by means of which they may be expeditiously 
raised and hung on hooks when it is necessary to attend to the 
water-vessels. The weight of the tubes is sufficiently great to 
