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Remarks on the "CIW" Vertical-Intensity Induction-Variometer
Mr. A. G. McNish of the Carnegie Institution of Washington has recently announced his newly designed vertical-intensity induction-variometer, finely making use of the two excellent magnetic properties of perminvar, a new magnetic alloy of iron, nickel and cobalt. His instrumental theory, however, seems insufficient and even goes astray in certain aspects.
The present author has computed the moment of force cast upon the armature by the field magnets, i.e. the induced cylinders of perminvar, and obtained a rather complicated formula with good reason, showing how to determine the size of the instrument. Then he proposes the π/4 - Z - variometer, so to speak, properly designed and adjusted that the maximum torque occurs always at the deflection angle π/4, and the equilibrium equation shall be rigorously expressed as KZ2cos2φ=Ｔ(t+φ) which has a great many advantage in practice. It is worth specially to mention above all that the ideal condition having the least values of the level effect as well as the deflection term in the scale-value equation may be thus reached with success, while high sensitivity may hardly be secured in spite of Mr. McNish’s analogy.
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