1^ EXPEllIMENTS OU 



EXPERIMENT III. 



I first applied a ret-hot bar of iron, as close to the 

 stem as could be coutrived without burning it, which 

 moved it uniformly from inght to left. 



Again, having prepared another stem, I applied 

 the steam of hot water, issuing from the spout of a 

 tea-kettle ; which caused it to move, with great vio- 

 lence, several revolutions from right to left : which 

 was a sufficient proof, that heat acted on this grass 

 only in as much as it deprived it of its moisture. 



I then proceeded to ascertain, whether the stem 

 was any way regularly affected by the changes in the 

 atmosphere ; a point on which every thing depended. 

 With this view I made up three hygrometers, on the 

 following construction : 



Three stalks were taken, of the same length and 

 number of twists, and, being fixed at one end into 

 a piece of wax, with an index (as above described) 

 the whole was fixed at the bottom of so many strong 

 tin boxes, about 2^ inches deep, on the edge of 

 which was placed a moveable broad pasteboard 

 circle, graduated eveiy 5^, and divided in the com- 

 mon way of 360°*. These three hygrometers were 

 then placed together, and observed, for two succes- 

 sive days, at every hour of the day, from 7 o'clock 

 in the morning to 8 in the evening; noticing at the 

 same time both the barometer and thermometer, as 

 the annexed tables will shew. 



* This graduation will, I trust, appear perfecllj sufficient, when 

 it is considered, that the mere effluvia arising from perspiration 

 moved the index 88 or 108, as above mentioned. 



