HOMER E. CHENOWETH. 



this account as well as on account of its small size that we de- 

 scribe it here though a better device is described by Hamilton 

 ('17) in the paper which follows. It is a well-known instrument, 

 and consists essentially of two parts, a tube pointing upstream 

 against the flow of air or gas and which converts the sum of the 

 static pressure and velocity pressure into a head which may 

 be measured, and, as a second part, a means of determining the 

 static pressure alone. Although the Pitot tube has long been 

 known and used there is still much doubt in regard to its accuracy 

 and distrust of the results obtained by its use. The form of tube 

 shown in Figs, i and 2 has been generally adopted as being the 

 most reliable. 



The Pitot tube, as described, was sealed in a glass tube i| 

 inches in diameter and 30 inches long, and the connection made 

 from the leads of the Pitot tube to a ten-inch mercury column 

 manometer by means of a piece of one-half-inch rubber tubing. 

 This general arrangement is shown in Fig. I. After the ap- 

 paratus had been set up as shown in the sketch the tube leading 

 to the cage was inserted into the neck of the inverted 1 3-liter 

 bottle and the air turned on. This was done in order that the 

 scale 5 on the mercury manometer could be calibrated in rate 

 of flow of the air. Several such readings were taken for the range 

 of pressures to be used in the experiments, and a scale constructed 

 whereby the rate of flow in liters per minute could be had directly 

 by measuring the height of the mercury in the manometer. The 

 rubber tubing from the exit side of the measuring device was then 

 connected to the leads from the cages containing mice. Some 

 of the later experiments were performed with the equipment 

 described by Hamilton ('17). 



2. General Plan of the Experiments. 



The mice were put into the experimental cages and air of dif- 

 ferent evaporating poWer was secured by passing air of different 

 relative humidities or different temperatures, or at different 

 velocities through the different divisions of the cages. The 

 bottom of the cage was covered with leaves and in order to keep 

 the air from blowing them to one side melted paraffin was poured 

 on them. This was done to procure a rough surface as the mice 



