. Electric railway gazette . obbin a common steelpen and close the key. The pen is instantly drawn intothe bobbin. Hold the bobbin in a vertical position keepingthe circuit closed. The pen is supported in the centre of thecoil by some unseen force. Break the circuit by openingthe key. The pen falls out of the bobbin. We see from this experiment that the coil of wirepossesses actual mechanical power, which power is underperfect control by opening and closing the circuit of thecoil. June IS, 189S. STREET RAILWAY GAZETTE. 279 To investigate this matter a little further, place a pieceof paper over
. Electric railway gazette . obbin a common steelpen and close the key. The pen is instantly drawn intothe bobbin. Hold the bobbin in a vertical position keepingthe circuit closed. The pen is supported in the centre of thecoil by some unseen force. Break the circuit by openingthe key. The pen falls out of the bobbin. We see from this experiment that the coil of wirepossesses actual mechanical power, which power is underperfect control by opening and closing the circuit of thecoil. June IS, 189S. STREET RAILWAY GAZETTE. 279 To investigate this matter a little further, place a pieceof paper over the top of the coil when in a vertical position,and closing the circuit, sprinkle the paper with iron filings arrange themselves in a very peculiar manner,shown in Fig. 5. Repeat the experiment, laying the paperon the side rather than the end of the coil. The arrange-ment shown in Fig. 6 is produced. Now these filings would not have taken up their peculiarposition if some force had not directed them there. If we. should immerse the coil in glycerine, in which were ironfilings in suspension, we should find that these lines of forceare not confined to one plane, but spray out from the endsof the coil like the heads of a sheaf of wheat. The filings somewhat imperfectly arrange themselvesalong what are called magnetic lines of force. For conven-ience in calculation, these lines are assumed to exist andtheir number per square inch, as they issue from the endof the coil or electromagnet, as we may now call it, is ameasure of its strength. The theoretical number of linesis far greater than is shown by the crude method of filings. But we notice that all bobbins used on street carmotors have an iron instead of an air core. In order toinvestigate the value of these iron cores, slip an ironcore into the bobbin you have made, using soft ironwires of even length. Test the strength of the magnet withthe iron filings on the paper, and you will find it severalhundred per cent, str
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1895
