Fig. 56b. SOME USEFUL ELECTRO-MECHANICAL DEVICES

[Large illustration]

In conclusion take this bit of advice: don’t try to invent a new kind of electric current and don’t try to devise a new electro-mechanical movement for in either case you will waste your time. Every form of current and every kind of electro-mechanical device you will need for any machine which you may invent are at hand and ready for use. Fig. 56 shows a number of electro-mechanical devices and these will aid you in getting the result you want.

Books.—The books on physics listed on page 69 go deeply enough into the subject of static and current electricity and magnetism for all ordinary purposes of invention, but if you are interested in wireless and high frequency electricity then I would suggest that you read the following books:

Fig. 57. AN AMMETER FOR MEASURING CURRENT
Fig. 58. A VOLTMETER FOR MEASURING PRESSURE

Your Electrical Equipment.—Should your invention call for experiments in electricity, especially where the amount of current used is a factor, you should provide yourself with a good ammeter, as shown in Fig. 57, for measuring the current in amperes, and a volt meter, as shown in Fig. 58, for measuring the pressure, or voltage, in volts. (See [Appendix O].)

Where the resistance in ohms of a wire, or a circuit of any kind must be known a combined bridge and resistance box is the best way to make accurate measurements. Resistance boxes measuring from .001 ohm to 17.600 ohms can be bought of the L. E. Knott Apparatus Co., Boston, Mass., for about $18.00. It is shown in Fig. 59.