File:General physiology of muscles and nerves (1881) (14775324104).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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e wire through which the current flowsis wound in several coils round the needle. As eachcoil exercises a force tending to cause the deflectionof the needle, the deflecting force is increased ; and aninstrument of this sort is, therefore, called a multiplier.^In order to increase the sensitiveness of this still further,the attraction of the earth must be annihilated as faras possible, so that even weak currents are able to causedeflection. This is accomplished, for instance, by ar-ranging a fixed magnet above or below the magneticneedle, so that it acts on the latter in a direction con- If attention is paid to certain circumstances, which cannot bementioned in detail here, the same instrument can also be used tomeasure the strength of currents j it is, therefore, also called a gal-vanometer. THE MULTIPLIER OR GALVANOMETER. 161 trary to that of the attraction of the earth, and bycarefully bringing this magnet nearer until the actionof the earth is almost entirely cancelled. Or two mag-
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EiG. 37. A MeLTirnKR. netic needles, as similar as possible, are connected by afixed intermediate piece in such a way that the corre-sponding poles are turned in opposite directions. Asthe force of trravitation now tends to turn the two 162 PHYSIOLOGY OF MUSCLES AND NERVES. needles in opposite directions, the force of attractionof the earth-magnetism is entirely, or almost entirelyremoved, so that even very weak electric currents, ifcaused to pass round the needle in a suitable way, cancause a noticeable deflection of the needle. Fig. 37 represents a sensitive multiplier of a formwell suited for physiological experiments. The twoneedles are connected together, and are suspended bymeans of a thread of silk from the frame h h; the screwi serves to raise the needles to a proper height, so thatone of them can move freely within the coils of the wire,the other above the latter and over a graduated circle, bywhich the deflection effected by the current can be mea-sured. The very thin wire,

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