142 BOTANICAL GAZETTE [AUGUST 
introduces an error which becomes very large as the time interval 
between the reading of the instruments and the length of time and 
the amount of precipitation increases. The instrument recently 
described by Yapp (34) and by LivrncsTon eliminates the error 
last mentioned, but some weighing method, when available, will 
probably be more exact than any, since it alone can be employed 
in the measurement of evaporation from ice, snow, and growing 
vegetation. 
Of the instruments on hand, one was established as a standard 
in an open lawn freely exposed to the sun and wind on the campus 
near the University Observatory. It was placed in a manner to 
obtain readings on the saturation deficiency of the air at a height 
of 15 cm. above the soil surface. The atmometer remained in the 
care of Professor H. C. Lorp and his assistant Mr. KENDRIG, to 
whom the writer expresses his warmest thanks for their helpful 
interest. The records were taken three times daily in connection 
with the climatological observations called for by the U.S. Weather 
Bureau Service, and consisted of the reading of the depth of water 
remaining in a graduated container. The instrument continued 
in operation from May 21 to September 17, when an accident 
resulted in the breaking of the graduated retainer. Within a few 
days the trouble had been remedied and the observations pro- 
ceeded until October 11, when the first heavy frost occurred. 
Another cup was placed in an open and exposed place in the 
cranberry-sphagnum (central) zone, under conditions similar to 
those of the standard instrument. It was installed May 14. 
With the exception of the period from June 11 to July 17, when 
the total for five weeks was recorded, the loss of water by evapora- 
tion was determined at intervals of one week by running in dis- 
tilled water from a graduate, thus restoring the original water 
level of the container. Records were obtained until August 21, 
when it was found that the atmometer had been disturbed. A 
week later it had disappeared entirely. No attempt was made 
to replace it by another. 
The third instrument stood in the shaded conditions of the 
maple-alder zone. It was placed near large-sized maples whose 
cover was relatively dense though open. The reading of this 
