Dept. Bull. 1136, U. S. Dept. of Agriculture PLATE 10 
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AIR-OPERATED EXTENSION-TUBE RECORDER CONTROLLER WITH A POROUS- 
SLEEVE TYPE WET BULB 
As the name implies, recorder controllers perform two separate functions; one is to record tempera- 
ture, and the other is to controlit. The instrument illustrated is of the double type, being equipped 
with two entirely separate recording and controlling mechanisms; both records, however, are made 
on the same chart. When arranged as shown here, with a wet bulb and a dry bulb close together, 
the instrument functions as a temperature and humidity recorder and controller, and is named 
“humidity recorder controller’? by the maker. Since the two operating systems are independent, 
it would be quite possible to use them for entirely unrelated purposes. The instrument is set by 
moving the two pointers, at the left of the two pens, to the desired temperatures, as indicated on the 
chart. When the instrument is functioning and the temperatures are under control, the pens ride 
directly over their respective pointers. The adjustment of the pointers is made from outside the 
case, by turning the winding Key at the right of the case, directly over the padlock. 
