. Student's manual of electro-therapeutics, embodying lectures delivered in the course on therapeutics at the Woman's medical college of the New York infirmary. ns. A long conductor, a conductor ofsmall diameter, or a poor conductor increasesthe external resistance ; while a short conduc-tor, a conductor of large size, or a good conductorlessens the external resistance. The unit of re-sistance is called an Ohm, and is equal to theobstruction to the passage of the electric cur-rent offered by a copper wire i mm. in dia-iheter and metres long, or a column ofmercury 1 sq. mm. in area and
. Student's manual of electro-therapeutics, embodying lectures delivered in the course on therapeutics at the Woman's medical college of the New York infirmary. ns. A long conductor, a conductor ofsmall diameter, or a poor conductor increasesthe external resistance ; while a short conduc-tor, a conductor of large size, or a good conductorlessens the external resistance. The unit of re-sistance is called an Ohm, and is equal to theobstruction to the passage of the electric cur-rent offered by a copper wire i mm. in dia-iheter and metres long, or a column ofmercury 1 sq. mm. in area and metres high. Sufficient electro-motive force to overcome anohm of resistance is the unit of electro-motiveforce, and is called a Volt. The current strength or working power of acell varies directly as the electro-motive force,and indirectly as the resistance. Thus representing the current strength by c,the electro-motive force by e., and the internal 8 ELECTRO- THERAPE UTICS. and external resistances by ir. and er., respect-ively, we have the proposition enunciatingOhms law, c. = ^ ^CT-, and by this formula allelectrical problems are worked out. Fig. 3. In the construction of batteries several cellsare used, arranged in various ways. When thepositive element of one is united to the negativeof the next, and so on, the cells are said to bearranged in compound circuit (see fig. 3). When F,c. 4
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