102 



NE'GfefcTTl AND ZAMBEA, HOLBOKtf VIADUCT, B.C., 



NOTE. -Any one not familiar with Metric Dials must observe that the figures read 

 rationally : thus, if the feet hand is at, say, nine, the tens hand will be near the figure it is 

 approaching. This figure must not be taken, but the previous one that is passed. 



Table showing the number of miles per hour at velocities per minute. 



" When inquiring into the causes of air currents, either from or within drains, it was 

 suggested that the variable flow of sewage has a powerful influence on the air within the 

 drain, whilst that produced by rainfall has still greater, and the variations of temperature 

 are another cause of displacement and renewal of drain air. A series of observations were 

 taken at the outlets of drains by the Anemometer at the point of connection with the 

 sewer, and the results proved that up and down currents of air are constantly passing to and 

 fro. Whenever an up-current issues through a drain-opening it must be manifest that some 

 of the inlets of such drains are untrapped. and therefore sewer air must be escaping through 

 such untrapped inlets, to the danger of those who reside in the house." 



142. Biram's Anemometers, for registering the velocity of currents of 

 air in mines, &c., by means of a light vane, the revolutions of which are 

 recorded npon a dial in the centre of the instrument. 

 12-in., 5 0; 6-in., 4 0; 4-in., 3 3 0; 2J-in., 2 10 



These Anemometers will register the velocity of Air through any passage 

 of a Mine or Air Shaft in which they are placed. 



'For the purpose of trying and regulating the proportions of Air to the 

 several divisions of a mine, and for the convenience of Overlookers, the three 

 small instruments, 6 inches, 4 inches, and 2J- inches, are recommended. These 

 sizes will also be found convenient for use in large gun or rifle practice. 



To ascertain the rate at which air is moving, proceed thus suppose 

 100 revolutions=200 feet per minute. 

 88] 200 [2^27. 



Say 2J miles per hour 88 being l-60th of a mile. 



To find the force of Wind, multiply the square of the velocity of the wind 

 in feet per second by "0023. 



NOTE. The velocity of the wind in feet per minute, divided by 88, will 

 give the velocity in miles per hour. (See above example.) 



