Bui. 1136, U. S. Dept. of Agriculture. 
Plate II, 
Fig. I. — Heater Unit for External Blower. 
Fig. 2. — Two-Pen Extension Tube Recording Thermome- 
ter Sectioned and With Chart Removed. 
The bulbs B are connected to the instrument through the armored tubing T 
entering at the top of the case. The pens P and pen arms are slightly to the 
left of the center. 
