Electrical measurementsA laboratory manual . at the needles, and so lessens the sensibility or thedeflection for a given current. 74. Calibration of any Galvanometer by Compar-ison with a Tangent Galvanometer/ — Connect a tan-gent galvanometer T, the galvanometer to be calibrated(r, a battery B^ and a suitable resistance i^, in series (). Note the deflections of both T and G; vary the current by changing .R,and again read the de-flections. The resistancesshould be varied or so ad-justed that the deflectionsof (r may be as nearlyas possible if the constant ofthe tangent g
Electrical measurementsA laboratory manual . at the needles, and so lessens the sensibility or thedeflection for a given current. 74. Calibration of any Galvanometer by Compar-ison with a Tangent Galvanometer/ — Connect a tan-gent galvanometer T, the galvanometer to be calibrated(r, a battery B^ and a suitable resistance i^, in series (). Note the deflections of both T and G; vary the current by changing .R,and again read the de-flections. The resistancesshould be varied or so ad-justed that the deflectionsof (r may be as nearlyas possible if the constant ofthe tangent galvanometerhas been determined pre-viously, the currents inamperes corresponding to the various deflections of Grare known. Construct a plain elastic curve, with cur-rents as abscissas and deflections of G as will be the calibration curve of G-, from which may beread off the currents corresponding to other deflections. If the constant of T has not been determined, thecalibration of Gr will be only relative and not absolute;. Fig. 72. Ayrtons Practical Electricity, p. 58. MEASUBEMENT OF CUBEENT. 151 that is, the deflections serve merely to compare currents,but not to measure them in amperes. It may happen that G- is more sensitive than T. Inthat case a suitable deflection of T produces too great aone in G. The difiiculty may be avoided by putting ashunt or by-path around (7, indicated at S. The calibra-tion Avill then be relative, unless the ratio of the resist-ances of G- and S is known. Example. G Tangent Gtalvanometeb. Currents (2). (2) -:- (1). Deflections (1). Deflections. Tangents. 50 ° 10 11 15 6 95 20 9,8 25 30 16. 35 40 The curve (Fig. 73) expressing the relation between deflec-tions and currents is plotted as described above. 75. Relative Calibration o
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