RESEARCH METHODS IN STIDV OF FOREST ENVIRONMENT. 35 



ing, and the upper end should he capped, the suspending cord being 

 attached to the inside of the cap. A welded pipe may he driven in 

 almost any soil if the upper cap is screwed on tightly, and a mallet 

 is used in driving, or wood is placed hetween the cap and hammer 

 used. An iron hammer directly applied will tear the cap to piec< - 

 in a few blows. 



The conductivity of an iron pipe is so great that its use for soil 

 temperatures at a depth of 1 foot or less introduces serious com- 

 plications. Wood or porcelain tubes are therefore necessarv. 



A porcelain wall tube, such as is commonly used in wiring build- 

 ings, may ordinarily be obtained in lengths up to one foot or more 

 at electrical supply shops. 



For a relatively permanent installation of thermometers at a 

 depth of about a foot, wood tubes turned and bored in a wood- 

 working shop are very satisfactory. The tube should have some 

 taper, and the lower end should be pointed, so that it may be driven 

 into a smaller hole that has been made with a bar. A wood which 

 does not split readily should be used. When completed, the tube 



Fig. 1.— Sectional view of turned wood tube for soil thermometers at a depth of 1 foot. TchtluTmoscope 

 (electric resistance thermometer) with one bulb and recording galvanometer $245; extra bulbs, each $15; 

 connecting wire, per foot about SO. 10. 



and its plug should be boiled and cooled in a bath of creosote and 

 linseed oil to prevent swelling, shrinking, and cracking. The top 

 of the tube may be turned with a slope outward, and the plug simi- 

 larly turned, so that rain water does not enter readily. A tube which 

 has proven very satisfactory in Forest Service work is shown in 



Figure 1. 



A satisfactory tube for temporary use may be made by cutting a 

 piece of 2 by 2 inch lumber 14 inches long, boring a 1-inch hole 

 through from end to end, capping the lower end with a piece oi 

 tin, and cutting a plug to fit in the opening at the top. Two inches 

 of the tube should be left above ground. It is hardly feasible to 

 prepare this apparatus in greater lengths; in fact, for depths ol 2 

 feet or more, the iron pipe is to be preferred. 



In order to obtain reliable readings with a thermometer which 

 must be lifted to read, it is necessary that the bulb ot the ther- 

 mometer be in some way protected from immediate contact with the 

 air. This is done either by placing it in a cork, by wrapping it in 



