A laboratory manual of electrotherapeutics . = current X potential difference) sup-plied to the machine and that yielded by it should beequal. The old method of controlling dynamo currentsfor cautery work by introducing heavy wire resistance in 66 LABORATORY MANUAL circuit is both very cumbersome and expensive since lessthan 10 per cent, of the energy is usefully employed. A similar waste of en-ergy can be obviated bycharging storage batter-ies with the transformedcurrent instead of em-ploying the ordinary dy-namo current controlledby resistance. A suitable rheostatmust be employed inthe caute
A laboratory manual of electrotherapeutics . = current X potential difference) sup-plied to the machine and that yielded by it should beequal. The old method of controlling dynamo currentsfor cautery work by introducing heavy wire resistance in 66 LABORATORY MANUAL circuit is both very cumbersome and expensive since lessthan 10 per cent, of the energy is usefully employed. A similar waste of en-ergy can be obviated bycharging storage batter-ies with the transformedcurrent instead of em-ploying the ordinary dy-namo current controlledby resistance. A suitable rheostatmust be employed inthe cautery or light cir-cuit for the purpose ofcontrolling the currentmore accurately. The rotary transform-er is not only a convenient and economical means for securing a direct currentfor therapeutic purposes but it is also a safe means. Whentaking a supply of current for therapeutic purposes fromdynamo mains carrying a current of high voltage all dangerof subjecting a patient to an excess of current or voltageis entirely removed by this Fig 34. Rotary Transformer. MAGNETISM. A close relationship exists between current electricityand magnetic phenomena. Induced current electricity,which plays a very important part in therapeutics, is theresult of magnetic action. There is also good reason tobelieve, from the results of recent investigations, thatmagnetism itself has some direct therapeutic value. Atleast we have discovered from experiments conducted fora number of months in this laboratory that the growth ofgrowing animals is accelerated when subjected for sometime to the influence of alternating magnetie fields. Theseconsiderations render it advisable for us to review byexperiment the fundamental phenomena relating to therelationship between electricity and magnetism. In performing the following experiments certain factsshould be kept in mind: i. Rough and careless handling of a permanentmagnet is very detrimental to its strength and may destroyits usefulness; 2. The swingi
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