The Astrophysical journal . for the instrument No. 2used below, in place of the desired width of 2 mm, the followingvalues : Right strip Left strip : mm mm ^•s- Mean Since the coating with lampblack leaves the edges a triflerough, an error of in the measures of the width evi-dently cannot be avoided, which in the width of the strips hereused may make an error of per cent, in the final value. In order to determine the resis-tance of the strips, I have used theelectrometric method, which hereoffers striking advantages. Thearrangement of this experi
The Astrophysical journal . for the instrument No. 2used below, in place of the desired width of 2 mm, the followingvalues : Right strip Left strip : mm mm ^•s- Mean Since the coating with lampblack leaves the edges a triflerough, an error of in the measures of the width evi-dently cannot be avoided, which in the width of the strips hereused may make an error of per cent, in the final value. In order to determine the resis-tance of the strips, I have used theelectrometric method, which hereoffers striking advantages. Thearrangement of this experiment isseen in Fig. 4. From the galvaniccell 5 a current is sent through thepyrheliometer strip F G, and a cali-brated wire of German silver ormanganin of accurately known re-sistance. From the two knifeedges A and B, and from two contacts H and /, which are inconnection with the strijjs and the wire, and of which / is asliding contact, wires go to the commutator VV, and from hereto the Lippmann capillary electrometer Fig. 4. ELECTRIC COMPENSATION PYRHELIOMETER 337 The arrangement of the knife edges 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
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
