September 15, 1916] 



SCIENCE 



397 



sleeping cars. Outside the realm of hygiene, 

 it is often unsuitable, for example for deter- 

 mining relative humidity among the stems and 

 leaves of seedling plants. 



by the obvious and simple method of using 

 a motor-driven fan, but also a graphic record 

 of the readings is kept. 



If a continuous record is not desired, it is 



a. Dry cell. 6. Key. c. Tube leading to water reservoir, d. Motor, e. Dry- 

 bulb thermometer. /. Wet-bulb thermometer, g. Fan. h. Water 

 reservoir, fc. Direction of air current. 



To obviate these difficulties, there have been 

 put upon the market within the last two or 

 three years mechanisms in which not only is 

 the ventilation of the wet bulb accomplished 



obvious that the fan ventilation of the thermom- 

 eter bulbs presents no mechanical difficulties 

 and offers some advantages over the sling 

 method. 



