EGGS IN COLD STORAGE. 



25 



in connection with the tables of hu- 

 midity published by the bureau, any 

 needed results may be obtained with 

 a fair degree of accuracy. The sling 

 psychrometer, as illustrated, consists 

 of a pair of thermometers mounted 

 on an aluminum plate, one higher 

 than the other, the lower having- its 

 bulb covered with a small sack of 

 muslin. At thetop, the frame or plate 

 supporting- the thermometers is pro- 

 vided with a handle for whirling-, this handle 

 being- connected by links to the plate, and 

 provided with a swivel to allow of a smooth 

 rotary motion. The bulb of the lower ther- 

 mometer is wet at the time of making- an ob- 

 servation, Ihe muslin serving- to retain a film 

 of water, surrounding- and in contact with 

 what is known as the wet bulb of the psy- 

 chrometer. The muslin should be renewed 

 from time to time, as the meshes between the 

 threads will gradually fill with solid matter 

 left by the evaporation of the water and the 

 natural accumulation of dust from the air. 

 The muslin in this condition will neither ab- 

 sorb nor evaporate the water readily. 



To make an observation dip the muslin Directionsfor 



using 1 the sling 



covered bulb in a small cup or other wide-P s y chrometer - 

 mouthed receptacle containing- water. Whirl 

 the thermometer for ten or fifteen seconds, 

 then dip the wet bulb of the psychrcmeter 

 into the water again. Whirl again for ten or 

 fifteen seconds, stop and read quickly, read- 

 ing- the wet bulb first. Repeat once or twice, 

 noting- the reading- each time. When two 

 successive readings of the wet bulb agree 

 very nearly, the lowest point has been 

 Dip the wet bulb only after the 



f 



SLING 

 PSYCHRO- 

 METER. -reached. 



