The London, Edinburgh and Dublin philosophical magazine and journal of science . f conductors wereeffected, but the results were not wholly satisfactory. Thereseemed to be some uncertainty in the determination of resis-tance, due to the inclusion of the two movable contacts of theresistance-slide in one of the sides (P) of the quadrilateral*.I therefore pass on to describe a slight modification by meansof which much sharper measurements were attainable. In order to get rid of the objectionable movable contacts,some sacrifice of theoretical simplicity seems can no longer keep Q (
The London, Edinburgh and Dublin philosophical magazine and journal of science . f conductors wereeffected, but the results were not wholly satisfactory. Thereseemed to be some uncertainty in the determination of resis-tance, due to the inclusion of the two movable contacts of theresistance-slide in one of the sides (P) of the quadrilateral*.I therefore pass on to describe a slight modification by meansof which much sharper measurements were attainable. In order to get rid of the objectionable movable contacts,some sacrifice of theoretical simplicity seems can no longer keep Q (and therefore P when a balanceis attained) constant ; but by reverting to the arrangementadopted in a well-known form of Wheatstones bridge, wecause the resistances taken from P to be added to Q, and viceversa. The transferable resistance is that of a straight wireof German silver, with which one telephone terminal makescontact at a point whose position is read off on a dividedscale. Any uncertainty in the resistance of this contact doesnot influence the measurements. Fig. The diagram shows the connection of the parts. One ofthe telephone terminals goes to the junction of the (-J ohm)resistances R and S, the other to a point upon the dividedwire. The branch P includes one compensator (with coilsconnected in series), the subject of examination, and part ofthe divided wire. The branch Q includes the second com-pensator (replaceable by a simple coil possessing suitable * Prof. Hughes appears also to have met with this difficulty in hissecond apparatus. Resistance of Compound Conductors. 483 self-induction), a rheostat, or any resistance roughly adjust-able from time to time, and the remainder of the divided battery branch, in which may also be included the in-terrupter, has its terminals connected, one to the junctionof P and R, the other to the junction of Q and S. When it isdesired to use steady currents, the telephone can of course bereplaced by a galvanometer. In
Size: 3237px × 772px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
