45, CORNHILL, E.G., AND 122, EEGENT STREET, '\V., LONDON. 



101 



And the real velocity during the running of ten minutes is 6620 feet. 



The measurement of the current of air in feet per minute, divided by 88, will give the 

 measurement or velocity in miles per hour. 



NOTE. In taking a measurement the fans must always face the wind, and care should 

 be taken not to bend or injure them. 



Price of the Improved Air Meter in a neat Box, figs. 110 and 111 440 



141. Lowne's Patent Colliery Air 

 Meter constructed expressly for use in Coal 

 Mines or Air Shafts. 



The improvements consists of 1st, 

 a large clear Dial; 2nd, the Fan is con- 

 structed of a light and anti-corrosive material ; 

 3rd, the Indicating parts are perfectly pro- 

 tected from dust and smoke (this is done by 

 a practical mechanical arrangement) ; and, 4th, 

 a Lever is placed in a convenient position, to 

 enable the observer to throw the Indicating 

 "Wheels in or out of gear from the Fan, 

 for the purpose of taking short ^observations 

 with accuracy-, 6-inch Air Meter, as fig. 112, Price, 4 10 



FIG. 112. 



INSTRUCTIONS FOR USINO THE IMPROVED AIR METER. 



Press the Lever home to the left hand, and the Fans will revolve without moving the 

 Registering Works. Now take a careful reading of the instrument, and write it down ; 

 hold the Air Meter in the current by the ring at the top of the Instrument ; allow the Fans 

 to run freely for a short time. Now observe the Watch. When the Second Hand reaches 

 the Minute, press the Lever to the right, and the works will be in gear. When the minute 

 is up, again press the Lever to the left hand, to throw the works out of gear ; take a reading 

 of the dial and write it down above the first reading, subtract the first reading from the 

 second, and the difference, after the correction is added, will be the velocity of the current 

 in feet per minute, thus : 



Second Reading 9,260 



First Reading . 8,920 



Add Correction, say 



Rate of current 



340 

 40 



380 feet per minute. 



For measuring currents for a longer space of time, the Air Meter should be suspended 

 on a bar, or fixed in any convenient manner in the current. 



The Fans must always face the current, and great care should be taken never to stop 

 them suddenly. 



