FREE BOOKS

Author's List




PREV.   NEXT  
|<   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76   77   78   79   80   81   82   83   84  
85   86   87   88   89   90   91   92   93   94   95   96   97   98   99   >>  
of each of the magnets shall freely enter the respective bores of the two bobbins fixed upon the same plate, and, when the whole system is in equilibrium and the bobbins free from current, the two branches of each of the magnets shall nearly coincide with the axes of such bores. The magnets are not plane, but are curved so as to form portions of a vertical cylinder whose axis coincides with the direction of the suspension wire, and to which the axes of the bobbins are tangent at their center, approximately to the points where the poles of the magnets are situated. [Illustration: FIG. 1. GRAY'S GALVANOMETER.] The needles have been given this form so that their extremities shall not touch the sides of the bore during considerable deflections. In the instrument which the inventors, Messrs. T. & A. Gray, used in their experiments upon the resistance of glass, the needles were arranged so that their poles of contrary name were opposite. [Illustration: FIG. 2.] The system of needles is suspended from the extremity of a screw, p, which passes into a nut, n, movable between two stationary pieces. On revolving the nut, we cause the screw to rise or lower, along with the entire suspended part, without twisting the thread. The four bobbins are grouped for tension, and have a total resistance of 30,220 ohms. They contain 16,000 feet of No. 50 copper wire, forming 62,939 revolutions, nearly equally divided between the four bobbins. When a current is passing through the bobbins, the poles of one of the horseshoe magnets are attracted toward the interior of the corresponding bobbins, while those of the other are repelled toward the exterior by the two other bobbins. We thus have a couple which tends to cause the system to revolve around the suspension axis. A mirror, which is fixed upon a vertical piece of aluminum, a, gives, in the usual manner, a reflected image upon a scale, thus allowing the deflections to be read. A compensating magnet, M, is supported by a vertical column fixed to the case, above the needles. This magnet may be placed in the different azimuths by means of a tangential screw, t. The extremities of the bobbin wires are connected with three terminals, T, T', T squared, and the instrument may, by a proper arrangement, became differential. These terminals, as well as the communicating wires, are insulated with ebonite. Thus arranged, the instrument is capable of making a deflection of one division of
PREV.   NEXT  
|<   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76   77   78   79   80   81   82   83   84  
85   86   87   88   89   90   91   92   93   94   95   96   97   98   99   >>  



Top keywords:

bobbins

 

magnets

 

needles

 

instrument

 

vertical

 
system
 

suspension

 

deflections

 

extremities

 
Illustration

suspended

 
terminals
 

magnet

 

current

 

arranged

 

resistance

 

revolve

 

couple

 

mirror

 

revolutions


passing

 

equally

 

divided

 

horseshoe

 

attracted

 

repelled

 

exterior

 

forming

 

copper

 

interior


proper

 
arrangement
 

differential

 

squared

 

bobbin

 
connected
 

making

 

deflection

 

division

 

capable


communicating

 

insulated

 

ebonite

 

tangential

 

allowing

 

reflected

 
manner
 

aluminum

 

compensating

 

azimuths