45, CORNHILL, B.C., AND 122, REGENT STREET, W., 



LONDON. 



105 



V 



FIG. 115. 



This Anemometer is furnished with two graduated circles, the outer one 

 being divided into five miles and tenths of a mile, and each division on the 

 inner circle represents five miles. One revolution of this circle recording from 

 five to five hundred and five miles. The fixed pointer or index recording on the 

 outer circle miles and tenths of a mile to five miles ; and the moving index 

 records every five miles up to five hundred. If for example the movable hand 

 stands between 15 and 20 on the inner circle, and the fixed hand indicates 3 

 miles and five-tenths the length of the current of air which has passed the 

 station is equivalent to 18 miles and five-tenths. 



The velocity of the wind at any particular moment is found by observing 

 the index before and after a certain interval of time as one or five minutes, and 

 then multiplying the rate by 60 or 12 to find the velocity in miles per hoar. 



The pressure in Ibs. per square foot can then be ascertained by reference to 

 tables mentioned in our list of books at the end of this Section. A mill-headed 

 screw at the back of the instrument (fig. 89) turns the movable index, which 

 should be brought back to zero after the observation is registered. 



Price, fig. 115, 4 10 



The Anemometer frame is arranged for screwing on the instrument to a 

 firmly-supported post. 



146. Robinson's Anemometer, (fig. 116). This drawing shows a further 

 improvement in the recording movement, a second dial being added for the 

 convenience of obtaining extended readings. 



The left hand dial of this Anemometer is divided and figured exactly the 

 same as in the previously described instrument, and the indications read off in 

 a similar manner. The second dial has 10 divisions, each of these divisions 

 being equal to 505 miles, which is sub-divided by the readings of the left hand 

 dial. Price, fig. 116, 6 15 



