METEOROLOGICAL INSTRUMENTS. 



147 



Inches. Pounds. 



4 - 20.833 



0.5 - 2.604 

 0.1 - 0.521 



The sum is 23.958, which expresses the force of the 

 wind when the height of the water in the gauge is 4.6 

 inches. 



Any alteration that can usually take place in the tempe- 

 rature of the water, makes no sensible difference in this in- 

 strument. 



In frosty weather this gauge cannot be used with common 

 water. At that time some other liquor must be used, which 

 is not subject to freeze ; and, upon the whole, a saturated 

 solution of common salt in water is the most eligible ; but in 

 that case (since the specific gravity of a saturated solution 

 of salt is to that of pure water, as 1.244 to 1) the forces 

 which are stated in the preceding table miist be multiplied 

 by 1.244. Thus, if in the preceding example the saturated 

 solution of salt had been used instead of water only, the 

 force of the wind on a square foot would have been 29.8 Ibs. 



When salt-water is used, the force of the wind, which is 

 stated in the table, must be increased in the proportion of 

 the specific gravity of salt-water to that of common wa- 

 ter ; thus, using the preceding example, we must say, as 

 1 : 1.244 : : 23.958 to a fourth proportional, which must be 

 found by multiplying the second term by the third, and then 

 dividing the product by the first term ; but, the first term 

 being unity, we need only multiply 23.958 by 1,244. 



Price, $6.00 to $8.00. 



Dr. Cumming's Statical 

 Thermometer. (Fig. 625.) 

 An instrument intended as a 

 mode of opening windows and 

 ventilators in apartments, by 

 the variations in temperature 

 of the included air. 



A is a tube and ball, either of 

 glass or iron, the ball being 

 capable of holding four or five 

 pints of air, and the tube, B, 

 about twenty-five inches long. 

 A portion of the tube is filled 



Fig. 625 



