66 



as much as possible its extension or contraction by 

 the changes of the atmosphere. 

 Fig. 3. The wooden pipe or tube two inches square, fastened 

 on the top of the pole aa. Fig. 1. open on the side, 

 to shew the manner that the sliding rod b passes 

 over the brass rollers fff, when the wind is suffi- 

 cientl}"^ strong to lift up one pound by its force on 

 the square surface presented to it, as (6) and (c), 

 Fig. 4. 



4. The wooden pipe or tube, in which are inclosed the 

 sliding rod, rollers, and line, from the effects of the 

 weather. 



5. The wooden frame, made of light wood, one foot 

 square, covered over with very thin sheet brass, 

 strongly painted, and varnished with copal. This 

 frame is fastened to the sliding rod b. Fig. 3. by 

 means of a mortice, &c. 



6. An enlarged view of the scale and index, which marks 

 the greatest force of the wind during the absence of 

 the observer, which is attached to the frame confin- 

 ing the weights, as gh. Fig. 2.; and being connected 

 with the hand fastened on the top weight {d. Fig. 2.) 

 raises the small Aveight (e); and this being counter- 

 poised by another of equal weight, by means of a 

 line passing over a small puUy, as represented by this 

 Fig. and also c. Fig. 2. occasions the small weight, 

 with its index, to stop at the number of pounds 

 raised by the force of the wind, though they should 



fall 



