Minor Constituents of Air 



237 



the experiment. Starting again from 0, mark out 

 similarly a scale of weights on the vertical line, the 

 numbers indicating grams and fractions of a gram. 

 To obtain the point corresponding to the first pair of 

 observations taken, note the point on the vertical scale 

 which represents the loss of weight experienced by the 

 water during the first day. From this point draw a 

 faint horizontal line to meet the vertical line from the 

 figure " 1 " on the time scale. Make a small dot at 

 the intersection of these lines and surround it by a 

 small circle. Each successive point is obtained in 

 similar fashion, the horizontal line from the point on 

 the scale of grams which indicates the loss of weight 

 during any given day being drawn to meet the vertical 

 line from the number representing the corresponding 

 number of days that have elapsed since the beginning 

 of the experiment. Join the various points thus found 

 by short straight lines as indicated ^ 



in the figure. 



(Note. The results obtained 

 will be more strictly comparable 

 if sufficient water be added each 

 day to that remaining in the vessel 

 to compensate exactly for the loss 

 of weight noted.) 



This experiment may well be 

 performed in conjunction with 



EXPERIMENT 100. Fig. 76 re- 

 presents an instrument called a 

 " wet and dry bulb hygrometer " 

 (moisture-measurer) . 



One of the thermometers is an 

 ordinary thermometer mounted on 

 a wooden frame, and the other is an exactly similar 



