260 NATURE-STVD1 REVIEW [6:9-^Dec, Wio 



II. Temperature 



(a) Dry-bulb thermometer 



(b) Wet-bulb thermometer 



(c) Maximum since previous reading 



(d) Minimum since previous reading 



III. Humidity 



( a ) Difference between dry and wet bulbs 



(b) Dew-point 



( c ) Saturation percentage 



IV. Pressure 



Temperature and Humidity. For the junior grades the 

 adjectives "very hot," "hot," "warm," "temperate," "cool," 

 "cold," "very cold," may be used. For other reasons than for 

 use in nature lessons every schoolroom should have a thermome- 

 ter. An additional one with exposed bulb which may be cov- 

 ered with cotton batting, dipped in water and swung around in 

 the air or kept stationary with the free end of the cotton 

 immersed in a bottle of water, will serve for a wet-bulb. Tables 

 can be obtained from the meteorological stations giving formulae 

 and ratios for working out the dew-point and the percentage of 

 saturation. Maximum and minimum thermometers which may 

 either be combined, as in Six's pattern, or separate — for nature- 

 study I prefer the latter — must be purchased. Dealers in green- 



