42 A MONTANE EAIN-FOREST. 



in 1903 to observe the effects of a prolonged season of dryness, but the 

 chance to secure soil-moisture determinations for such a period has not 

 recurred since I have been interested in the subject. 



My instrumentation has, accordingly, centered in the determination 

 of the atmospheric moisture conditions, extending also to the securing 

 of air and soil-temperature readings. Automatic traces of the daily 

 play of the humidity conditions were secured by use of a hygrograph, 

 which was combined with a thermograph in the type of double register 

 made by Friez. Owing to the practical exigencies of the work, only 

 one of the instruments was used, which was moved from place to place 

 to secure the several records, thereby making it impossible for me to 

 obtain simultaneous readings from different stations. The general 

 uniformity of the weather conditions through the winter of 1905-06 

 kept this circumstance from seriously impairing the comparableness 

 of the various record slips. The instrument was installed about 3 feet 

 from the ground, on a portable framework of boards, and protected 

 by a white water-proofed canvas placed so as to be at least 1 foot from 

 the instrument above and at the sides, while the ends, together with the 

 open base, gave a free access of air. A soil thermograph of the Hallock 

 type, made by Friez, was also used, being usually installed with the 

 double register or else in a similar manner. The cylinder was buried 

 at a depth of 1 foot in all cases; a hole was dug, from which a tunnel was 

 made to one side for the cylinder, and the earth was packed in naturally. 

 In this manner the soil above the cyhnder was left undisturbed. 



The hydrograph was corrected at the beginning and end of each week 

 in accordance with sling-psychrometer readings. The thermograph 

 was also verified in its reading twice for each sheet; the soil thermo- 

 graph three times for the period of five months over which it was used. 

 The thermograph and hygrograph traces presented in the accompany- 

 ing plates have been redrawn from the originals. This has lost them 

 something of their detail, but has been necessary to the incorporating 

 of the corrections, as well as to the manner of their reproduction. 



During the summer of 1909 a number of readings were taken at 

 Cinchona and in the rain-forest with the type of atmometer devised by 

 Livingston.^ The atmometers were protected from rain by suspending 

 a small pane of glass horizontally at a few inches above the tip of the 

 cup. The error due to the wetting and impact of rainfall in the ordi- 

 nary atmometer when not covered by glass is considerable, and is most 

 satisfactorily obviated by the use of the rain-correcting type of instru- 

 ment more recently invented by Livingston.^ Readings with an instru- 



'Li vingston, B. E. The Relation of Desert Plants to Soil Moisture and to Evaporation. Carnegie 

 Inst. Wash. Pub. SO, 1906. Also: Operation of the Porous Cup Atmometer. Plant World, 

 13 : 111-119, 1910. 



'Livingston, B. E. A Rain-correcting Atmometer for Ecological Instrumentation. Plant World , 

 13 : 79-82, 1910. 



