Makcfi 1, 1886.] 



KNO\VLEDGE 



157 



together, and placed on the prime conductor, electricity 

 ■will, wlien the machine is worked, pass up the spiral, and 

 so to the points, where, on escxping, it produces a 

 perceptible wind, having sufficient force to drive the 

 " electric mill" round in the opposite direction to that of 

 the points. 



A .simple form of electric mill mny be made by sticking 

 a needle, eye downwards (N, Fig. 5), into the end of a dr}^ 

 wooden rod or a stick of sealing-wax (A), and balancing 

 on the point, the moving portion consisting of two or 

 three straws (S S), iibout eight inches long, .stuck together 

 at their centres with sealing-wax, r.nd furnished with fine 

 wires passing through the straws, and bent at their 

 extremities so as to produce the " points," all of which 

 should be turned in the same direction. A small 

 piece of straw or a fine glass cone (made by heating a 

 piece of glass tubing, drawing it out, and cutting the part 

 off for the cone) being fastened to the junction of the 

 straws by means of sealing-wax completes the apparatus, 

 which may be worked from the table by connecting the 

 needle with the prime conductor, and turnin» the 

 niachiue. 



Fig. 6. 



In Fig. 6 is illustrated another simple piece of appa- 

 ratus dealing with the effect of points. A wooden base 

 measuring about nine inches by five is provided, and is 

 fitted at one end with glass rods a quarter of an inch in 

 diameter and about eight inches long, the other end 

 being fitted with similar rods five or six inches long. 

 Straightened pieces of wire are attached to the upper 

 ends of the rods as shown in the diagram either by being 

 soldered to brass caps fitted on to the glass, or they maj' 

 be simply stuck on with a little sealing-wax. A third 

 and very efficient mode of fixing is to fit paper tubes 

 three-quarters of an inch long over the tops of the rods, 

 and passing the wires through holes made for the pur- 

 pose in the sides of the tubes (about half their length 

 being left about the rods), to fill up with a cement com- 

 posed of equal parts of powdered resin and beeswax melted 

 together and mixed with a somewhat larger proportion of 

 red ochre. The next thing is to make the mill, which 

 should consi-st of four pieces of thin wire, each three and 

 a half inches long and bent at the ends at right angles 

 (as shown). A small thin metal disc drilled at the centre 

 should be fitted to a piece of wire stout enough to form 

 the spindle, and the bent pieces soldered to its sides, as 

 little solder as possible being used, and care being taken 

 to keep the mill as nearly balanced as possible. The mill 

 being placed on the lower ends of the inclined wires, and 

 these wires connected with the prime conductor, the dis- 

 charge of electricity from the points will cause the mill 

 to revolve, and in so doing to ascend the inclined plane. 

 Obviously the mill must be placed on the wires with the 

 points in the direction shown in the diagram. 



A sheet of note-paper may be made to yield both in- 

 terest and instruction. To the knob (c, Fig. 7), on the 

 wire attached to the prime conductor (or to the conductor 

 itself) attach a stout wire of any convenient metal, bent 

 to the shape shown, the end B being turned iip so as to 



form a hook. Over this hang a sheet of foreign note or 

 tissue paper cut into narrow strips. On turning the 

 machine, the strips flj- apart by mutual repulsion. If 

 the hand bs broncrht near attraction towards it results; 



Fig. 7. ; 



the same is observed if a needle be approached (side- 

 ways), so long as it is covered by the finger, but if the 

 finger be withdrawn, the strips will be blown away, 

 although if the needle be held upright under the hook, 

 so as to be opposite the centre of tlie ta.ssel, discharge 

 ensues, and the strips fall together (as in Fig 8). 



Fig. 8. 



The principle involved in this exj)eriment is a highly 

 interesting one and, properly understood, is capable of 

 rendering intelligible manj- of tlie apparently more intri- 

 cate experiments and many of the phenomena pertaining 

 to atmospheric electricity. To some of these latter our 

 attention will next be directed. 



A highly interesting and simply constructed piece of 

 apparatus is that illustrated in Fig. 9, where A B is a 

 piece of stout wire, eight or nine inches long, provided 

 at its ends with small conducting balls, either of metal 

 or of wood, &3., coated with Dutch metal or tin foil. 

 From the ends two-inch bells, C, D, are suspended by 



