To show how the apparatus at the various stations is arranged to correspond with the disks of various sizes attached to the front of the carriers, a diagram, Fig. 41, has been made, in which the needles at the bottom of the receiving tubes of the apparatus at six intermediate stations are represented at A, B, C, D, E, and F. Six disks of different sizes are represented at _a_, _b_, _c_, _d_, _e_, and _f_. The needles are placed farthest apart at station A and nearer together at each succeeding station until we arrive at station F, where they are nearest together. If we wish to send a carrier to station A from the central, we place the largest disk, _a_, upon the front end of it. When it arrives at station A, it closes the electric circuit between the needles and is discharged from the tube. Should we wish to send a carrier to station D, then we place the disk _d_ upon the front end of it. When the carrier arrives at the station A, the disk is not large enough to span the needles; therefore the sluice-gate is not opened and the carrier is sent on in the tube. When it arrives at stations B and C, the same thing occurs again, but when it reaches station D, the needles are sufficiently close together so that the disk makes an electric circuit between them, and the carrier is discharged from the tube, as was intended when despatched. Since the carriers always travel in the same direction in a tube, the first station at which they arrive where the needles are near enough together to have both touch the disk, will be the station at which the carrier was intended to stop. Carriers can be despatched from any station, but if we wish to send from say D to A, they must either travel around a loop or be sent through a return tube in which the needles are arranged in the reverse order. If no disk is placed on the carrier, it will go to the last station on the line. There are other attachments that might be made to the front end of the carriers in order to have them stop at any desired station along a line. We have worked out two other systems which are entirely mechanical in their operation, not using electric circuits and electro-magnets to move the valves. While such a mechanical system has some advantages over the present combined mechanical and electrical system, yet there is one great advantage in the latter, and that is the simplicity of the attachment made to the carrier. A round flat disk of tin-plate is attached to the front end; it is something that is not in the way; it does not prevent standing the carriers on end in racks to fill them; it is not easily injured, and only those who have had experience can realize the rough usage that the carriers receive; it is quickly and easily attached to the carrier, and it is so cheap that when bent it can be thrown away.