244 



Mean Direction of the Wind. 



the period during which the record indicated identically the same 

 direction of the wind ; and lastly, the number of hours during this 

 interval when the pressure apparatus showed the wind to blow with a 

 force of at least eight ounces on a plate ten inches square. 



Table VII. — Instances of remarkably steady Winds. 



Force of the Wind. 



The force of the wind was recorded by an anemometer constructed 

 upon the principle of Osier's anemometer, from directions furnished 

 by Dr. Smallwood of Montreal.* The pressure plate was ten inches 

 square, and the spring was a straight steel rod, 2 ft. 7 in. long, and 

 one-fourth inch in diameter. The weight of the clock (the same as 

 employed for recording the direction of the vane) turned a horizontal 

 cylinder nine inches long, and three and three-quarter inches in diam- 

 eter, with a uniform and known velocity. A long roll of paper, eight 

 inches broad, wound upon a roller, passed over the cylinder, and was 

 wound up on another roller. The ends of the cylinder were armed 

 upon its circumference with sharp points, which caught the paper and 

 carried it forward with the same velocity as that with which the 

 cylinder turned. The motions of the pressure plate were communi- 

 cated by means of wheel work to a pencil, whicli was pressed by a 

 sj)ring against the paper. When the pressure plate was stationary, 

 the pencil described a straight line upon the paper ; l)ut when the 

 plate was in motion, the pencil traced a zig-zag line. 



Before the commencement of the observations, experiments were 

 made to determine the amount of pressure on the plate corresponding 

 to given jiositions of the spring ; and hence the distance of the diifer- 

 ent points of the zig-zag line from tlie line of no pressure, could be 

 converted into ounces of pressure on a surface ten inches square. 

 Unfortunately these experiments were not repeated at the close of the 

 observations. In the course of the two years during which the spring 



* See page 209 and note. 



