ANEMOMETER 



178 



It has been stated by some writers that there is a difference between the force or 

 impulse of air moving upon a body at rest, and the resistance which a body moving 

 through a still atmosphere meets with in its passage, supposing the velocity to be the 

 same in each case ; and besides this, the effect of a body moving in a circle, in a still 

 atmosphere, may not bo the same as when moving in a straight line. The experiments 

 of Hutton and others appear, however, to indicate that the force of impact of a wind 

 against a stationary body is always proportional to the resistance which a solid, moved 

 through a still atmosphere, meets with at the same velocity. 



A valuable series of experiments were made with this instrument by the late Mr. 

 Atkinson, one of her Majesty's Coal Inspectors, and Mr. John Daglish, for. which we 

 must refer to the Transactions of the North of England Institute of Mining Engineers. 

 The Tables that are given in connection with the Memoir there published are of the 

 highest possible value. 



Water-gauges are sometimes used in determining the rate at which air passes 

 through the shafts or galleries of a mine. They are ordinarily U-shaped tubes with a 

 measured quantity of water, one limb of the tube being bent down, so as to be presented 

 to the current of air. ^ 



The anemometer of Dr. Lind resembles the photometer of Pitot ; it determines the 

 velocity of the wind by its action on a small quantity of water in a U-sh&P e( l tubq. 

 As the same instrument is much used in coal mines as a water-gauge for indicating 

 the difference of pressure between the down-cast and up-cast air-column, it will not be 

 at all necessary to give a detailed description of it. From numerous experiments, Dr. 

 Lind considered that the pressure of the wind in direct impulse is nearly proportional 

 to the square of its velocity. ..; 



Mr. John Daglish, F.G.S. introduced certain improvements in the construction of 

 the water-gauge, which he communicated to the Manchester meeting of the North of 

 England Institute of Mining Engineers, July 14th, 1865. : 



This communication was made in the following words : 



' Every one who has been much occupied in 

 conducting experiments on the ventilation of 

 mines will have probably felt the inconve- 

 niences attending the use of the ordinary form 

 of water-gauge. 



1 The form of water-gauge introduced by Mr. 

 Daglish, and now extensively in xiso in tho 

 North of England, is constructed with special 

 regard to portability, accuracy, and endurance. 



' As the maximum pressure seldom exceeds 

 three inches of , water-column, it is not neces- 

 sary that the travel of the index-scale should 

 exceed this; the scale is divided simply on 

 either side into inches and tenths, the pressure- 

 markings on the scale of the ordinary water- 

 gauge being not only useless but confusing, 

 and prevent tho accurate determination of the 

 difference of the level of the water in each 

 tube. The upper end of one of the tubes is 

 bent over, and open to the external air only 

 by a contracted aperture. This prevents the 

 passage of dust into the tube, which is a fruit- 

 ful source of annoyance in tho ordinary water- 

 gauge when placed permanently in exposed 

 situations in dusty mines. The scale is moved 

 by a threaded rod working through a female 

 screw attached to the scale : this insures not 

 only tho accurate adjustment of the scale in the 

 first instance, but its retention in sit-u, when 

 adjusted. In the ordinary form, if the brass spring-clips^which attach the scale to 

 the tubes, bo too strong, tho scale cannot bo accurately adjusted, especially when the 

 water column vibrates much ; if, on tho other hand, they are too weak, the scale will 

 not remain in sitii, but falls when released, and this latter is always the tendency after 

 much use ; and \mless the tubes are perfectly parallel, the scale will be too stiff in 

 one position, and fall in another. Tho upper end of the other txibe is bent at right 

 angles and fitted up with a short piece of flexible tubing, to the other end of which is 

 attached a short brass tube to be inserted into the aperture to which it is required to 

 attach tho water-gauge; this short piece of interposed flexible tubing . between the 

 rigid brasg and glass prevent* the liability to fracture of the tubes, in fixing the 



