The Astrophysical journal . dges A and B is seen in These are fastened at the ends of a small glass tube E, whichis suspended from an ebonite plate H by spiral wires. This jjlatecan be lowered by means of a screw, and sothe knife edges can be pressed lightly on thestrips. Since the sliding contact is so regu- j^-\ ? -rr^^v~^^ fflated that the potential differences betweenA and B and between //and /are the same,the resistance of the strip between the pointsA and B is directly determined. Bv thismethod of determination, the disturbances atthe ends of the strips are eliminated, and theresi
The Astrophysical journal . dges A and B is seen in These are fastened at the ends of a small glass tube E, whichis suspended from an ebonite plate H by spiral wires. This jjlatecan be lowered by means of a screw, and sothe knife edges can be pressed lightly on thestrips. Since the sliding contact is so regu- j^-\ ? -rr^^v~^^ fflated that the potential differences betweenA and B and between //and /are the same,the resistance of the strip between the pointsA and B is directly determined. Bv thismethod of determination, the disturbances atthe ends of the strips are eliminated, and theresistance determined in the part of the strip Fig. 5. lying close to the junction of the thermo-element. The platinum strips are heated by the passage of the current,and accordingly the resistance increased. By investigating theresistance for currents of different strenorths, the relation betweenthese two magnitudes can be approximately determined. Accord-ingly, for instrument II at 19°, the following results wereobtained :. Stren gth ot current Resistance in ohms per cm / r- Observed Calculated Since the heating of the strips is proportional to the squareof the strength of the current, we have, if in, and m\^ are theresistances for currents of strength / and 0, mi^=ni\ (i -]- /3/). The values of ;«, in the above table, calculated according tothe above formula from the values w^ = and /3 = ,show with certainty that this method of measuring leads to verygood results. 33S Axrr AAcsTJWj/ The temperature coefficient ot the electric resistance of thestrips is found in the ordinary manner by means of a Wheatstonebridge. The formula m\ = vi,, (i +u/) gives here a satisfactory degree of precision. For tiic platinummaterial used I have found a ; and this gives ///; Denoting bv the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
