Injury, recovery, and death, in relation to conductivity and permeability . lwork and there is no object in striving to get greateraccuracy than this in the apparatus itself. It is usually desirable to introduce a variable capaci-tance or an arrangement such as is suggested by Taylorand Curtis (1915), by Taylor and Acree (1916) or byMcClendon (1920). In the writers experiments thecapacity of the apparatus, filled with living Laminariaand lifted out of the sea water, was about one thousandthof a microfarad. An advantageous arrangement suggested by Profes-sor G. W. Pierce is shown in Fig. 6. The
Injury, recovery, and death, in relation to conductivity and permeability . lwork and there is no object in striving to get greateraccuracy than this in the apparatus itself. It is usually desirable to introduce a variable capaci-tance or an arrangement such as is suggested by Taylorand Curtis (1915), by Taylor and Acree (1916) or byMcClendon (1920). In the writers experiments thecapacity of the apparatus, filled with living Laminariaand lifted out of the sea water, was about one thousandthof a microfarad. An advantageous arrangement suggested by Profes-sor G. W. Pierce is shown in Fig. 6. The frequency is of some importance. The writerhas found a thousand cycles convenient; this may beobtained by means of an ^^audio oscillator (such asis used in wireless telegraphy) as furnished by theGeneral Radio Co., or bv means of a toothed iron wheel re- 30 INJURY, RECOVERY, AND DEATH volving in a suitably arranged magnetic circuit such asis furnished by Leeds and Northrup. The results soobtained did not differ from those secured with aVreeland oscillator. S WWW- 5000 n. Fig. 6.—DiaRram to tbow bridge and connections. S is an alternating source (1000 cyclesor more), A and B are the ratio arms of the bridge, C is the variable resistance of the bridge,X is the unknown resistance (tissue and holder), T, telephone, V, variable condenser, G, aground wire from the centre of a high resistance (in case the ratio arms of the bridge areunequal the two parts of the high resistaKce should also be unequal). The use of the ordinary lighting circuit (60 cycles)with a vibration galvanometer is recommended by Green(1917). The use of an alternating current galvanom-eter in connection with a recording device is suggestedby Weibel and Thuras (1918). MEASUKING ELECTRICAL CONDUCTIVITY 31 For details regarding apparatus the reader is re-ferred to the papers of Hibbard and Chapman (1915),Washburn^^ Taylor and Acree^^, Rivers-Moore (1919),Schlesinger and Reed (1919), Newberry (1919), Hall(1919), and
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