It is very desirable in medical work to eliminate the noise attendant upon the working of the coil vibrator. This jarring or humming is often in itself a source of irritation to a nervous patient. The sound can be deadened in various ways, for instance, by placing over the vibrator a temporary wood cover, lined with felt, resting upon a soft rubber gasket; or in any other manner that may suggest itself to the operator.
TABLE SHOWING RESISTANCES AND FEET PER POUND OF COPPER AND GERMAN SILVER WIRES.
——————————+————————-+——————-++——————————-++——————————- | | || COPPER. || GERMAN | | || || SILVER. Gauge, | | ++——————————-++——————————- Browne |Diameter.| Feet || || ONLY & Sharpe. | |per lb.|| Ohms ||APPROXIMATE. | | || per ++——————————- | | || 1,000 ft. || Ohms | | || ||per 1,000 ft. ——————————+————————-+——————-++——————————-++——————————- 8 | .1285 | 20 || .62881 || 11.77 9 | .1144 | 25 || .79281 || 11.83 10 | .1019 | 32 || 1 || 18.72 11 | .09074 | 40 || 1.2607 || 25.59 12 | .08081 | 51 || 1.5898 || 29.75 13 | .07196 | 64 || 1.995 || 37.51 14 | .06408 | 81 || 2.504 || 47.30 15 | .05707 | 102 || 3.172 || 59.65 16 | .05082 | 129 || 4.001 || 75.22 17 | .04525 | 162 || 5.04 || 94.84 18 | .0403 | 204 || 6.36 || 119.61 19 | .03539 | 264 || 8.25 || 155.10 20 | .03196 | 325 || 10.12 || 190.18 21 | .02846 | 409 || 12.76 || 239.81 22 | .02535 | 517 || 16.25 || 302.38 23 | .02257 | 660 || 20.30 || 381.33 24 | .0201 | 823 || 25.60 || 480.83 25 | .0179 | 1039 || 32.20 || 606.31 26 | .01594 | 1310 || 40.70 || 764.59 27 | .01419 | 1650 || 51.30 || 964.13 28 | .01264 | 2082 || 64.80 || 1215.76 29 | .01126 | 2623 || 81.60 || 1533.06 30 | .01002 | 3311 || 103 || 1933.03 31 | .00893 | 4165 || 130 || 2437.23 32 | .00795 | 5263 || 164 || 3073.77 33 | .00708 | 6636 || 206 || 3875.61 34 | .0063 | 8381 || 260 || 4888.49 35 | .00561 | 10560 || 328 || 6163.97 36 | .005 | 13306 || 414 || 7770.81 ——————————+————————-+——————-++——————————-++——————————-
The simple form of contact breaker already described is useful up to a certain point, but it has disadvantages. Its rate of vibration is only variable through narrow limits, and it is not suitable for very heavy currents. But as it stands it has done long service, and will be used probably wherever the requirements from it are not exacting. The most desirable form of this simple spring break is shown in Fig. 18. _R_ is the soft iron armature; _S_, the spring; _C_, check-nut which holds the adjusting screw _A_ from becoming loose; _T_, a second adjusting screw used to tighten the spring and so raise its rate of vibration; _K_ is the base to which one wire of the coil is attached; _L_, base of adjusting device to which battery wire runs at _I_. Where tightening screw T passes through the pillar of the adjusting screw, the hole therein is bushed with rubber to prevent accidental contact. Both _A_ and _T_ are provided with insulating heads of rubber or ivory. At _B_ are the platinum contacts, which should be fully ⅛ inch in diameter.