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. If 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- 



