378 Eighth Annual Report of the 



2. A continuous record of temperature is furnished by a Richard 

 thermograph placed in the slielter. The pen tracing the record 

 is attached to an ann whose position is governed by the expan- 

 sion or contraction of a metal tube filled with alcohol. The record- 

 ing sheet is carried by a cylinder, revolved by clock-work, at the 

 rate of one turn per week. This thermograph, which is very accu- 

 rate when i)roperly adjusted, is checked by comparison with the 

 adjacent standard thermometer. , 



Hygrometers. — The shelter also contains a hair hygrometer 

 (Richard's), whose registering mechanism is similar to that of 

 the thermograph; but in this case the pen arm is moved by the 

 expansion and contraction of a bundle of hairs which are 

 rendered very sensitive to the action of moisture by a special 

 process of the makers. The index or datum of this hygrometer 

 is liable to change somew^hat during prolonged wet or dry 

 periods; but gives very satisfactory results when adjusted from 

 time to time to agree with the values of humidity indicated by 

 the whirled psychrometer. (See " Instructions to voluntary ob- 

 servers " for full information regarding the latter instrument.) 



A Richard dry and wet bulb recording hygrometer has also 

 been used at this station, but thus far has not proved as satis- 

 factory as the instrument just described. In principle it con- 

 sists of two Richard thermographs, one of which has its alcohol 

 tube moistened constantly by muslin dipping into a reservoir, 

 while the other tube is kept dry. The instrument is so con- 

 structed, however, that the records of both dry and wet bulbs are 

 traced upon the same cylinder. 



Evaporometer. — An evaporometer (Richard's) is located beneath 

 the shelter at a height of 2 feet from the ground; direct sunlight 

 and driving rain or snow being excluded by louvred sides. The 

 evaporometer consists, essentially, of a pair of scales, one pan of 

 which carries the water, whose evaporation is to be measured, 

 and a pen attached by suitable mechanism to the scale arm, 

 which records on a rotating cylinder the rise or fall of the scale 

 beam as the quantity of water is diminished or increased. 



