RESEARCH METHODS IN STUDY OF FOEEST ENVIRONMENT. 35 



ing. and the upper end should be capped, the suspending cord being 

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

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

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

 used. An iron hammer directly applied will tear the cap to pieces 

 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 necessary. 



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 



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

 Telethermoscope (electric resistance thermometer) with one bulb and recording gal- 

 vanometer $245 ; extra bulbs, each $15,. connecting wire, per foot about $0.10. 



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 -Mt us factory 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 of 

 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 of 2 

 f<ii or more, the iron pipe is to be preferred. 



In order to obtain reliable readings with a thermometer whieh 

 mn-i be lifted to read, it is necessary that the bulb of the ther- 

 mometer be in some way protected from immediate contact with the 

 air. Tin i- done either by placing it in a fork-, by wrapping it in 



