I20 DESIGN IN NATURE 



The dynamo can, in some cases, produce sparks five feet long, and these are beheved to be identical with discharges 

 of lightning. In some cases the time occupied by the oscillations of electric sparks is less than one ten-nulhonth 

 of a second. " In hghtning discharges high electro-motive force and great quantity are frequently combmed m 

 a very short interval of time." A diagram of a series dynamo is given at Fig. 24. 



Electricity, when made, can be stored by conducting it to a storage battery. " The storage battery or 

 accumulator in its commonest form consists, before it is charged, of red oxide of lead with electrodes of lead. 

 The oxide and the electrodes are suitably immersed in dilute sulphuric acid, a*id a strong current of electricity is 

 sent from one electrode to the other. The oxygen resulting from the electrolysis of the water converts the red 

 oxide of lead at the future positive pole of the battery into peroxide of lead and into metalUc lead at the future 

 negative pole of the cell. When the charging current is removed and the peroxide of lead pole is connected with 

 the porous metallic lead pole, a current of electricity is produced, and the peroxide goes back to a lower oxide. 

 There are other batteries where peroxide of lead and zinc are employed, and from wluch more powerful 

 currents can be obtained. These have been advocated by Professor Main, and are known as zinc-lead storage 



j-iQ '("'f'.pTl pel 



The presence of electricity is detected by introducing a small bar-magnet (magnetic needle) or a galvanometer 

 into the magnetic field. The magnetic needle is composed of a slender bar of magnetised steel suspended at its 

 middle by a single fibre of untwisted silk, or set on an agate point, which leaves it free to move in a horizontal 



direction and also to dip at either end. This needle exhibits a north 

 and south pole, and arranges itself in the direction of the poles of the 

 earth. It sets or points towards a wire through which electricity is 

 flowing, and is thrown into vibration by any electrical disturbances in its 

 vicinity. The galvanometer is a still more deUcate and sympathetic in- 

 strument for detecting electrical currents. " It consists essentially of a 

 coil or bobbin of wire Uke a spool of thread, with a tiny magnet hung by 

 a spider thread near one end of the spool." It shows that " electrical 

 actions pervade all matter, and that there are electric waves in the ether 

 of space." It is in physics what the microscope is in anatomy and 

 physiology. By its use the faintest electrical currents are brought into 

 prominence, and their strength measured. The galvanometer is provided 

 with the hghtest possible bar-magnet or needle with hair pointers at either 

 end, a graduated scale, and two spools of thin insulated copper wire ; one 

 end of the one spool being connected with one end of the other, i.e. they 

 are connected in series. If one spool be placed on the stage of a micro- 

 scope bearing iron-filings on white paper, and the other spool be placed on 

 a third spool made of coarse wire, the ends of which are connected with 

 a battery, a glance at the microscope shows that when the battery current 

 is suddenly made or broken the iron particles vibrate, proving that currents 

 of electricity are passing in the circuit of wire on the two connected spools. The current set up by the battery can 

 at once be detected, and also in the wires and in the atmosphere investing the wires. " Any change in an electric 

 current on a wire, any pulsation, causes instantly a similar pulsation in any neighbouring wire not connected with 

 the first wire and placed parallel to it." 



The important part which electricity plays in the inorganic kingdom extends, as indicated, to the organic. 

 Siemens exposed certain plants to the rays of electric light for long periods, with the result that he greatly facili- 

 tated their growth. The effects of electricity as a curative agent, especially in nerve and muscular diseases, are well 

 known. Electricity, there is reason to beUeve, plays a leading role not only in structural development, but also in 

 functional processes and movements. 



Closely connected with electricity and Hght are the mysterious cathode, Eontgen, and other rays. These rays 

 have marvellous penetrating powers ; photographs being taken by their aid through various solid substances, such 

 as wood, metal, the tissues of the body, &c. 



The waves of electricity travel with the velocity of hght ; hght attaining to the incredible speed of 185,000 miles 

 per second. 



The discharges from a Leyden jar also travel at enormous velocities. Professor Joseph Henry has shown that 

 the discharge of a Leyden jar is oscillatory, and that induction efEects are produced by remarkably small quantities 

 of electricity. 



Fig. 24. — Series dynamo, x. Revolving com- 

 mutator with segments (c) ; h, V, brushes for 

 taking off the electric current ; a, iron ring with 

 coils of wire connected with segments (c) of com- 

 mutator (x) ; n, s, field magnets with north and 

 soiith poles. Positive electricity ( + ) is obtained 

 at b, and negative electricity { - ) at b'. The 

 current is made to flow round the field magnets 

 [n, s), so as to make north and south poles. 



Trowbridge, op. cit. p. 112, 



