64 



SCIENTIF'IC NEWS. 



[May 2nd, : 



tried, was so great that Mr. Brush designed the " Colossus/' 

 of our illustration, in order to meet the demands of the 

 larger furnaces which were constructed. We understand 

 that the machine was made complete in all its details, from 

 the specifications of its designer and inventor, and without 

 any preliminary trials ; and that when tested, it was found 

 to require no alteration of any kind, and came fully up to 

 the conditions of the contract. The fact that a dynamo 

 may be precisely designed and proportioned for any kind 

 and amount of work that may be demanded, whether for 

 electric lighting, electric smelting, or any other of the ap- 

 plications of electricity, is one of the most interesting and 

 important facts in connection with recent work in this field. 

 Another very valuable factor in the operation of this process 

 is the economy secured by the increased size of the dyna- 

 mos, it being stated that each new and larger machine has 

 very considerably reduced the price at which the metal or 

 alloys may be produced. 



In our illustration a smaller machine is shown. This 

 is the smallest Brush dynamo yet constructed on the 

 same model as the first machine made by Mr. Brush about 

 ten years ago. It was designed to supply a single arc light, 

 a duty which it performed satisfactorily without alteration, 

 exactly as it was constructed from the drawings. It is inte- 

 resting to note that there is no marked difference in the form 

 and principle of these two machines. 



Another electrical method for the production of aluminium 

 has been developed by Dr. Kleiner, of Zurich, who has worked 

 out the well-known laboratory experiment of the electrolytic 

 decomposition of the fused double chloride (cryolite) to what 

 appears to be a practical and successful process. Our 

 readers will no doubt remember that in 1807 Davy suc- 

 ceeded in decomposing potash and soda by passing an 

 electric current through them, and he thus succeeded for 

 the first time in obtaining the metals potassium and sodium. 

 Magnesium, and indeed all metals, can be separated from 

 their compounds by some modification of electrolysis, the 

 familiar operations of electro-plating being instances of the 

 most useful applications of this process. In the case in 

 point, cryolite, when brought to a state of fusion by heat, 

 may be made to give up its aluminium. Dr. Kleiner not 

 only decomposes the cryolite by electricity, after the man- 

 ner of ordinary electro-deposition, but he heats and fuses 

 the chloride by the same current which he uses to decom- 

 pose it. Both Messrs. Cowles and Dr. Kleiner use an 

 electric furnace, having carbon rods, from which the current 

 is conducted to the material to be acted upon, and dynamo 

 machines to produce the current ; but here the resemblance 

 ceases. Dr. Kleiner's process is distinctly an electrolytic 

 one, the current being made to perform the two functions of 

 decomposing the salt and depositing the metal, as in, an 

 electro-plating bath, at the same time that it produces suffi- 

 cient heat to bring the material into a fluid condition. A 

 comparatively low and quite ordinary temperature is all that 

 is required for the operation. 



The Cowles process, on the other hand, is a smelting pro- 

 cess, and owes its successful use of electricity to the fact that 

 by this means a temperature so high is attained that the 

 almost infusible corundum is made to part with its oxygen 

 and to give up its aluminium to form alloys with other 

 metals. 



How difficult it is to tear aluminium from its compounds 

 will be understood when it is stated that theoretically the 

 utmost amount of the metal that can possibly be obtained 

 by electrical energy equal to 100 horse-power, applied for 

 one hour, would be i lb. In practice it is not likely that 

 more than | lb. would be yielded per hour by an engine 

 giving 100 effective horse-power. Nevertheless, so valuable 

 is the metal that preparations are being made to carry out 



this electrolytic operation on a large scale. It will be evi- 

 dent that cheap power is desirable, and those concerned 

 in Dr. Kleiner's interesting process had acquired the rights 

 over half the falls of the Rhine at Schaffhausen, where it 

 was calculated that 15,000 horse-power could be obtained, 

 sufficient to produce 600,000 lbs. of aluminium per annum. 

 This bold scheme has, however, fallen through, owing to the 

 Government having declined to allow the power of the falls 

 to be used in this manner, as it was considered that the pic- 

 turesqueness of the locality would be seriously affected. This 

 decision, which must have carried comfort to the heart of 

 Mr. Ruskin if he has heard of it, has determined those inte- 

 rested in the process to start a large works in some part of 

 England where cheap coal can be obtained ; and to test the 

 process on a comparatively large scale by the employment 

 of steam-engines of about 500 horse-power. We wish 

 them all success in their important experiment. 



NOTES ON COLOUR. 



III. 



THE subject of colour may be treated up to a certain 

 point without the introduction of optical principles ; 

 but for the further consideration of several common appear- 

 ances, the explanation of which is not generally understood, 

 it now becomes necessary to say a few preliminary words 

 on a cognate subject. 



Sound is the effect on the ear of vibrations of invisible 

 and almost intangible air. Light is the effect on the eye of 

 vibrations of an invisible, intangible,and all but inconceivable 

 medium called ether, or aether. The conception of ether is 

 nothing new ; on the contrary, it is a survival from the times 

 when ethers were as plenty as blackberries. Ethers were 

 provided for planets to swim in ; for the transference of 

 " magnetic effluvia " ; to assist sensations of touch, etc. ; in 

 fact. Nature's abhorrence of a vacuum was sufficient reason 

 for imagining an ether. 



We are now taught that there is one ether, a medium 

 prevading all space — at all events as far as light travels, its 

 apparent use being to convey light and magnetism. These 

 two forces are closely connected, and though the form of 

 connection discovered by Maxwell has been questioned, the 

 same ether is probably the vehicle of both. Little resist- 

 ance as ether gives to the fall of a feather in a vacuum, or 

 to the motion of the planets, or the light and bulky masses 

 of comets, it must be considered to be a solid. It is, how- 

 ever, about 93,00 j,ooo,u^jo,Lu,o.,o,uoo,ajo of the density of water, and 

 yet about 1,000,000,000 times as rigid as steel, or nearly 

 300,000,000 times as rigid as glass. It is incompressible. 

 The only substance to which it can be coinpared is a thin 

 jelly. A disturbance is propagated in it as a vibration at 

 the rate of the velocity of light. This has been measured 

 in various ways, and the different results, made with greater 

 care and more exact methods, appear to approach more and 

 more to the value of 30,000,000 metres, or 186,400 miles 

 per second. The velocity of an electro -magnetic disturbance - 

 does not differ more from this quantity than the measure- 

 ments of various observers differ among theinselves. The 

 vibrations are not like those of sound, moving to and fro in 

 the direction in which it travels, but at right angles to its 

 path. 



Not only do the vibrations travel with this inconceivable 

 rapidity, but they follow each other at the rate of about five 

 hundred million million (500,000,000,000,000) per second. 

 Waves on a lake, travelling at a speed of 200 feet a minute, 

 and following each other at the rate of twenty a minute must 

 evidently be ten feet apart. This distance, measured from 

 crest to crest, or from trough to trough, is called a wave 



