TERRESTRIAL REFRACTION. 31 



Namely 290 

 +204 



Rev. 



494=1 + 134» 

 Whence it will appear, that since the index had mov- 



Rev. 



ed, by the application of heat, 2 + 105=825" 



and that, by cooling, it only recovered 1 + 134=494 



it follows, that the stem, by being de- 

 prived of its radical moisture, lost a 

 power =33 r 



EXPERIMENT V. 



Application of Moisture. 



As soon as the index of the same stem gave signs 

 of proceeding regularly with the hygrometers, a hair 

 pencil, full of water, was applied, and held to th% 



stem, when it revolved 6 + 295' from left to right, and 

 then remained quiescent. On the pencil being with- 

 drawn, the index began to recede, and resumed the 

 course of the other hygrometers, after revolving 



6+300'. 



But, during the interval of this experiment, thes« 

 had moved 135°, in the same direction with that 

 under observation, which quantity is therefore to be 

 subtracted. 



R. 



Namely 6+300 

 —135 



6+165 



Again, we have seen, that by the application of 



R. 



extreme moisture, the index had revolved, 6+295* 

 Hence, it will appear, that this process, 6+165 



affected the fibres of the stem by ' J30~ 



«3 



