9# EXPERIMENTS ON 



It may, however, be proper to mention, that not- 

 withstanding the great regularity which appears to 

 prevail between the rates of going of these hygro- 

 meters, whenever the atmosphere was unconimonh' 

 moist, the exquisite sensibility of the stem required 

 to be checked; for, as it would sometimes, during a 

 heavy shower, revolve a whole revolution, it was not 

 to be expected, that the three instruments would 

 keep pace, whilst moving so briskly. A silk thread 

 was therefore fastened at each end of the index, 

 loaded with a thin plate of lead, hanging loose on 

 the bottom of the box, so as to be dragged by the 

 straw as it went round. By these means the instru- 

 ments were easily regulated. 



EXPERIMENT TV. 



Application of heat, to determine the compass of 

 the instrument. 



Having fixed a stem, of six twists, in such a man- 

 ner as to admit it, I brought a bar of heated iron as 

 close to the stem as could be done, without setting 

 fire to the apparatus; on which the index revolved, 

 2 revolutions and 105°, from right to left, M'hen it 

 became quiescent. That is, the heat of the iron 

 affected it no longer in that direction, and wajt 

 barely sufficient to keep the index from falling back. 



The heated bar being withdrawn, the index began 

 to recede, and became quiescent again (that is in its 

 natural position) after having returned 290°. 



But the three hygrometers, A\diose rate of going is 

 given in the preceding table, had moved meanwhile 

 204° towards it; and therefore this quantity is to be 

 added to the above. 



