Recording Thermometers for Clinical Work, 563 



of the bridge-wire so as to give a range of from 35° to 

 45° G.j with a 1 ohm bridge-wire. 



Some observers have experienced trouble with this type 

 of recorder owing to the heating effect of the measuring 

 current. Such troubles have arisen chiefly from the employ- 

 ment of unsuitable thermometers with excessive currents. 

 "With a 26 ohm thermometer the instrument can be adjusted 

 to work perfectly on a scale of 4 cm. to 1° 0. with a current 

 of one hundredth of an ampere through the thermometer. 

 The record can be read easily to less than a hundredth of a 

 decree, or 1 in 30,000 ; and the heating effect of the current, 

 with a celluloid thermometer of the surface type above 

 described, is only two or three thousandths of a degree, or 

 practically inappreciable on the most open scale of the record. 



Testing and Adjustment of Slide-wire Recorder. 



11. The most important points to test in a slide-wire re- 

 corder are the adjustment of the zero of the galvanometer, 

 and the zero of the slide-wire. When the galvanometer 

 coil is free and the instrument levelled, the two prongs of 

 the contact fork should be just clear of the contact wheel on 

 either side. If there is any torsion in the suspension, one 

 of the prongs will bear against the wheel, and the pen will 

 travel continuously in one direction when the circuit of the 

 relay magnets is made, the galvanometer circuit being open. 

 The torsion head should be adjusted until the pen does not 

 travel either way under these conditions. This is a very 

 delicate test. If there is much torsion in the suspension, the 

 apparent zero on the slide-wire will vary to some extent 

 with the resistance in circuit when the galvanometer circuit 

 is closed. This adjustment is made before the instrument 

 is sent out, but it is desirable to test it occasionally, especially 

 if the suspension has been strained or damaged, or if a new 

 suspension is fitted. 



To adjust the zero of the slide-wire, short circuit the 

 pyrometer and compensator terminals, PP and CC, with 

 short equal pieces of copper wire. When the battery is 

 switched on the pen will quickly come to rest at the zero. 

 If the position is not quite correct in reference to the record 

 sheet, the slide-wire may be shifted in the direction of its 

 length through a distance equal to the observed deviation. 

 For many purposes it is most convenient to have the zero 

 in the centre of the slide-wire. The wire can then be 

 changed, if desired, for another of different resistance and 

 scale, without altering the zero. If it is desired to have the 



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