deabnessJ THE WEATHER AS NATURE-STUDY 261 



house or poultry supplies usually carry a stock of cheap hygro- 

 meters and thermometers of all kinds. 



Pressure. The smoking chimney has already been referred 

 to. The barometer should be introduced as soon as the pupils can 

 be brought to understand its principle and action. For the study 

 under discussion, one made in the schoolroom with a glass tube 

 about thirty-two inches long, three-eighths to a quarter of an inch 

 in diameter, and about a dollar's worth of mercury, is preferable 

 to the expensive instrument made at a factory. The open end 

 of the tube may rest in a bottle of mercury, — the tube itself main- 

 tained in the erect position by two or three tape-straps holding it 

 against the framing of a window. The graduation may be a 

 ruling in inches and eighths or tenths, or metric, as preferred, on 

 a strip of paper placed on the board behind the glass tube. 

 It is not important that the scale be placed exactly at the right 

 height since it is the rising and falling of the column, and rate 

 of change rather than its absolute length, which are noteworthy. 

 Barometric observations should be discussed in connection with 

 those made upon the ascent of smoke, the altitude of birds and 

 insects in flight, the reported feelings of rheumatic people, the 

 poise of certain tree-leaves, etc. 



Atmospheric Movements. The direction of the wind is 

 easily inferred from its effect upon clouds, smoke, dust, and 

 tree-branches, and these should be observed even when a vane 

 is visible. It is not diffcult to make a good wind-vane from two 

 thin boards, 6"x24", joined at their ends at an angle of 22 de- 

 grees, and poised to revolve on a central cross-piece where it can 

 catch the wind in every direction. 



The velocity of the wind may be very well expressed in 

 adjectives, those in common use being: 



Calm — Imperceptible movement. 



Light — Moving leaves of trees, — 1 to 5 miles an hour. 



Moderate — Moving slender branches, — 6 to 10 miles an hour. 



Brisk — Moving large branches, raising dust in the road, — 12 

 to 18 miles an hour. 



High — Swaying trees, raising loose objects, as twigs, — 20 

 to 30 miles an hour. 



Gale — Breaking branches, loosening old fence-boards, dif- 

 ficult to walk against, — 45 to 60 miles an hour. 



Hurricane or Tornado — Sweeping everything before it, — 80 

 to 200 miles per hour. 

 Directions for making a simple anemometer are given in a 



