96 SEC. 3. MEASUREMENT. 



397. Bevy's Current Meter, constructed for measuring the 

 velocity of currents in larger rivers. Elliott Brothers. 



The spherical boss is so determined that it will displace just as much water 

 as will balance the weight of all the parts which are fixed to the spindle, so 

 as to reduce friction to a minimum. Although the apparatus is covered 

 with glass, it has to be filled, before using it, with pure water to establish 

 similarity of pressure inside and outside. After every experiment the water 

 is removed and the spindle thoroughly dried. This form of current meter 

 was used by Mr. Bevy in the survey of the Parana and Uruguay rivers. 



39 7a. Darcy-Pitot Gauge or Current Meter, for deter- 

 mining the velocity of streams of water. Prof- W. C. Unto in. 



The velocity is obtained by a single measurement, and no time observation 

 is required. Used in Darcy and Bazin's researches on the flow of water in 

 pipes and canals. 



399. Water Meter, based on the principle of measuring the 

 volume of water by recording its speed. J. A. Mutter, C.E. 



This water meter consists principally of an air and water-tight chamber or 

 vessel, wherein moves a float, carrying two magnets of equal power, and fixed 

 with their dissimilar poles in juxtaposition to each other : the whole combina- 

 tion of the float and its spindle, together with the magnets, is made as near as 

 possible equal in density or specific gravity to the water. The water in pacing 

 through this measuring vessel is forced to take a rotary motion, by means of 

 a screen or a tongue, being a metal piece, put at a certain distance from the 

 inlet opening, and parallel with and lying along the inner circumference of 

 the measuring vessel. The top cover of the measuring vessel is p-operly 

 dished out, so a& to allow of two small soft iron armatures, fixed to a thin 

 metal arm or needle, to be brought outside the vessel, as near as can be to 

 the poles of the magnets inside; the metal arm or needle is fixed to a light 

 spindle, carrying an archimedean screw, which further gears with the regis- 

 tering parts of the apparatus. It is evident that the water in passing through 

 the measuring vessel, or rather alongside the same, communicates its motion 

 to the water inside the measuring vessel, which motion is also communicated to 

 the float and magnets, and lastly to the needle and worm spindle and further 

 gearing. It is plain that this meter really registers the true velocity of the 

 water, and taking, moreover, into consideration the lightness of its different 

 parts and the transmission of the speed of the float by means of magnets, it 

 will be found to be a very correct and sensitive meter, of simple and durable 

 construction. 



399a. Current Meter, with electrical tell-tale apparatus', 

 according to Amsler's latest construction. (See description.) 



Polytechnic School, Aix-la-Cliapelle, O. Intzc. 



If the instrument makes 100 revolutions the electric current will be closed 

 by a contact, and the chime work will be kept in motion during some revolu- 

 tions of the instrument ; it will not be necessary, therefore, in measuring the 

 velocity in water-courses, to pull the instrument out of the water, but only to 

 note the time which passes from one signal to the other. By experiments it 

 must be ascertained what velocities of the current of the water correspond 

 to certain intervals of time between the electric signals. 



400. Patent Electric Velocimeter, invented by Francis 

 Pastor elli, arranged for water currents, and for ascertaining the 

 speed of vessels. It consists of three parts. Francis Pastorelli. 



