44 THE HABITAT 
69. The weekly visit. Psychrographs must be visited, checked, rewound, 
and inked every week. Whenever possible this should be done regularly 
at a specified day and hour. This is especially desirable if the same record 
sheet is used for more than one week. Time and energy are saved by a fixed 
order for the various tasks to be done at each visit. After opening the 
instrument the disk is removed, and the clock wound, and, if need be, regu- 
lated. The record sheet is replaced, the disk again put on the clock arbor, 
and the pen replenished with a drop of ink. A psychrometer reading is 
made, and the results in terms of relative humidity noted at the proper 
place on the disk sheet. If the psychrograph vary. more than I per cent, it 
is adjusted to read accurately. In practice it has been found a great con- 
venience to keep each record sheet in position for three weeks, and the 
time may easily be extended to four. In this event, the pen is carefully 
cleaned with blotting paper at each visit, and is then refilled with an ink 
of different color. To prevent confusion, the three different colored inks 
are always used in the same order, red for the first week, blue for the second, 
and green for the third. The advantages of this plan are obvious: fewer 
records are used and less time is spent in changing them. The records of 
several weeks are side by side instead of on separate sheets, and in working 
over the season’s results, it is necessary to handle but a third as many 
sheets. 
The Draper psychrograph is made by the Draper Manufacturing Com- 
pany, 152 Front St., New York city. The price is $30. A few record 
sheets and a bottle of red ink are furnished with it. Additional records can 
be obtained at 3 cents each. The inks are 25-50 cents per bottle, depending 
upon the color. 
Humidity Readings and Records 
70. The time of readings. Ii simple instruments alone are used for 
determining humidity, readings are practically without value unless made 
simultaneously through several stations, or successively at one. When it is 
possible to combine these, and to make psychrometer readings at different 
habitats for each hour of the day, or at the same hour for several days, the 
series is of very great value. Single readings are unreliable on account of 
the hourly and daily variations of humidity, but when these changes are 
recorded by a psychrograph, such readings at once become of use, whether 
made in the same habitat with the recording instrument or elsewhere. In 
the latter case, one reading will tell little about the normal humidity of the 
habitat, but several make. a close estimate possible. When a, series of 
psychrographs is in use, accurate observations can be made to advantage 
anywhere at any time. As a rule, however, it has been found most con- 
