Popular Science Mouthlij
��box to a brass cup in the bottom. It is essential that tlic arrow swings easily on its pivot. The box should be 3 in. in height and 6 in. scjuare. In the bottom of the bo.\ twoconcenlriccirclesaredrawn. The annular ring between the cireles should measure i in. in width. In this ring, 8 curved metal plates are imposed. They serve as commutators. They should be screwed down perfectly flat and the screw- heads filed flush with the metal surface. An air -space of 3/16 in. should exist between the segments. There will be 8 segments altogether. To the outside rim of each of these a i-ft. No. 18 annun- ciator, or bell wire is soklered.
A metal arm, which ])resses down upon the plates with sufficient force to insure an electrical contact, is soldered on the pivot rod a short distance above its base. It is made from spring-brass 3^2 '•!• wide. To counteract its spring-like action, which otherwise would force the rod and the arrow upwards, a ring or flange shoukl be soldered to the rod immediately below the box cover. The tension of the swinging contact should then be adjusted so that, vhen the cover of the box is on, the arrow will swing freely, but at the same time the arm will make firm contact with the segments. To the metal socket into which the base of the rod fits, another i-ft. length of No. 18 annunciator wire should be soldered. The directions of the compass towards which each of the segments point should l)e indicated by tags on the wires which lead from them. This is important.
���The vane wit'i its slider-arm for mak- ing electric connections with the dial
Otherwise, confusion of an amusing variety will result when the dial is connected and the batteries are in circuit. A westerly wind may be registered as southeast, etc. Holes should be bored in the bottom of the box, to drain off rain water.
A cable of 9 annunciator wires, properly
��indicated by numbers or letters at the enil of each, should l)e made as follows : Stretch between 2 points, which are as far apart as the distance from the vane to the dial, the
���The wiring diagram showing the electrical connections between the vane and the dial
��9 annunciator wires. Tar them carefully and while the tar is still soft, wrap the "rope" with insulating tape. The cable should be properly connected to the 9 wires from the vane-segments and contact-arm and led to the room where the registering dial is to be mounted.
This consists of a polished wood box of the sanM* general dimensions as the box on tlrt!^"roof, but with 8 holes each i in. in diameter bored in a circle in its front side. A sheet of ground glass is placed against the holes underneath. The 8 directions of the compass are written in black ink on the glass which covers the holes. Under each hole a miniature electric lamp is mounted. The light corresponding to the vane segment which points north is connected to one post of the "north light." The remaining seven segments are connected to their correspond- ing lights on the dial. The remaining 8 posts of the lamp are connected together and the wire run to one pole of a gravity-, or blue vitriol, l^attery consisting of 3 fresh cells. The 3 cells are sufficient when the cable from dial to vane is no longer than 40 ft. For every additional 10 ft. another cell should be added. If the push button is used, dry cells, not gra\ ily cells, shoulil be employetl.
The ninth wire of the cable, the one which leads from the pi\-ot of the vane, is connected with the other side of the bat- tery. If the wind is from a northerly direc- tion, the north light of the dial will be lighted ; if in a southerly direction, the south light will show, etc. But if the wind should blow in such a direction that the arm on the pivot rests on two segments simultaneously, two adjacent lamps will light.— G. F. Worts.