_Apparatus._ A copper wire, C W (No. 44); insulating rubber band, R B (No. 45, Fig. 33); wire swing, W S (No. 37); the other half of the flat box, T F B (No. 41); apparatus of Exp. 69. =130. Telegraph Line.= To have our telegraph line using frictional electricity complete, we must have: (1) Some way of generating or making the electricity; (2) Some means of getting it or its effects to the other end of the line; (3) Some way of showing that it has been taken there. The charged E S will be the source of the electrification. New York will represent the end at which we _send_ the message, so at N. Y. we must have a _sending instrument_. See Fig. 33, which explains itself. R B or a silk thread must be used to _insulate_ the sender. Around one leg of W S is twisted one bare end of the _conductor_, C W. Boston will represent the end of the line at which the message is received, and there we need a _receiving instrument_. This is similar to the apparatus described in Exp. 69, Fig. 37. In addition to this, tie the middle of a moist cotton thread that is 6 in. long, to B C (Fig. 37), and let its two free ends lie over the top and reach down against the bottom of the tin; that is, on the left-hand side. Fig. 42 will give you an idea in regard to the looks of the thread; at first, however, it should be close to the bottom of the tin. Twist the other bare end of the copper wire around B C. When the line is properly constructed and ready for use, both instruments and C W are entirely insulated. Do not let any part of C W touch the table or your clothing. =131. Directions.= (A) Touch the insulated sending instrument with the charged ebonite sheet, and watch for any motion in the receiving instrument. =Note.= Better results will be obtained by using the charged electrophorus cover as the source of electrification, instead of E S. (Exp. 68.) _=132. Discussion.=_ The action here was like that in the previous experiment, the difference being that a longer _conductor_ was used. Electrification is always looking for some place to get to the earth, just as water will run from a roof to the ground. You will understand more about it a little later. In our apparatus just described, the only way that the earth could be reached was through the wooden rod S R. Do not get the idea that real messages are sent in any such way, or that electricity flows through a wire as water flows through a pipe. _=133. Relation between Conductors and Insulators.=_ The above terms are merely relative. Static electricity is easily conducted by dry wood, while Galvanic electricity is practically insulated by it. A substance may be an insulator for currents of low potential, while at the same time it will conduct high potential currents. (See Potential § 144.)