File:General physiology of muscles and nerves (1881) (14777682815).jpg

Identifier: generalphysiolo00rose (find matches)
Title: General physiology of muscles and nerves
Year: 1881 (1880s)
Authors: Rosenthal, I. (Isidor), 1836-1915
Subjects: Physiology Muscles Nerves
Publisher: New York, D. Appleton and company
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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owing to the moreperfect adaptation of another form of apparatus, calledthe tangent galvanometer, for such purposes. The ad-vantage of this consists in the fact that it is not onlyvery sensitive, but it also allows the strength of thecurrent to be measured. If, for example, the deflec-tions of the magnetic needle are very slight, the strengthof the currents may be regarded as proportionate to thetrigonometrical tangents of the angle of deflection. Inorder to measure slight deflections of this sort, ourformer method of observation by means of the mirrorand lens may be used (chap, iv., § 3, p. 57). Eitherthe magnet is in itself reflecting, or it is connectedwith a mirror, and is suspended by a silk thread in acopper sheath. A, which is closed by plates of looking- See Notes and Additions, No. 9. THE REFLECTING GALVANOMETER. 163 glass. The electric current can be transmitted throughthe coils B B, which move on slides, in oider that bytheir greater or lesser distance from the magnet, the
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sensitiveness of the instrument may be graduated atwill. In order to measure the deflections, a graduatedscale is placed parallel to the mirror when in its qui- 164. PHYSIOLOGY OF MUSCLES AND NERVES. escent position, and its reflection is observed throughthe lens as described in Chap. IV., § 3. This may alsobe used to render the deflection visible to a large audi-ence, by allowing the light of a suflficiently powerfullamp to fall on the mirror and throwing the reflectionon to a screen by means of a lens. In order to in-crease the sensitiveness of the instrument, the influenceof gravitation on the deflecting magnet is decreased, asalready described, by means of a properly arrangedmagnet. 5. Having, in one or other of these ways, providedas sensitive a multiplier as may be, all that is necessaryis to connect the animal substances which are to be ex-amined with this, and then to observe whether deflec-tion occurs or not; whether, that is, with the arrange-ment selected a current is pres

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