Septemiser 28, 1888.] 



SCIENCE. 



153 



agrees in this opinion, which is also the verdict of a commission 

 appointed by the medical congress held at Paris. The results an- 

 nounced by the Paris doctors were not obtained, and often were 

 replaced by directly opposite results. The experiments of all out- 

 side of Paris seem to be opposed to the alleged influence of the 

 magnet on hypnotic sensations. 



The Dreams OF THE Deaf. — In the course of an article on 

 dreams, etc., Mr. J. M. Buckley (Cenhcty, July, 1888) mentions 

 that he has at various times made inquiry as to the occurrence of 

 sounds in the dreams of the deaf, and found no such instance when 

 deafness set in before the fourth year of life. One correspondent 

 mentions that deaf people dream of hearing, if they became deaf 

 after learning to speak. The deaf are very sensitive to jars, waking 

 up by the beating of a bass-drum, and this class of sensations is 

 represented in their dream-life. These facts illustrate in a con- 

 clusive manner the dependence of the imaginative and constructive 

 powers upon the sensations, as well as point to the existence of an 

 era when this dependence is no longer necessary for the retention 

 of dream-fancy. 



ELECTRICAL SCIENCE. 

 Production of Light in the Future. 



The following very interesting extract from Prof. Oliver Lodge's 

 ' Modern Views of Electricity,' that has appeared in Nature, is 

 given in the London Ekclriciaii : — 



" The conclusions at which we have arrived, that light is an 

 electrical disturbance, and that light-waves are excited by electric 

 oscillations, must ultimately and very shortly have a practical im- 

 port. 



" Our present systems of making light artificially are wasteful 

 and ineffective. We want a certain range of oscillation, between 

 seven thousand and four thousand billion vibrations per second (no 

 other is useful to us, because no other has any effect on our retina) ; 

 but we do not know how to produce vibrations of this rate. We 

 can produce a definite vibration of one or two hundred or thousand 

 per second : in other words, w-e can excite a pure tone of definite 

 pitch, and we can command any desired range of such tones con- 

 tinuously by means of bellows and a key-board. We can also 

 (though the fact is less well known) excite momentarily definite 

 ethereal vibrations of some millions per second, but we do not at 

 present seem to know how to maintain this rate quite continuously. 

 To get much faster rates of vibration than this, we have to fall 

 back upon atoms. We know how to make atoms vibrate : it is 

 done by what we call ' heating ' the substance ; and if we could 

 deal with individual atoms, unhampered by others, it is possible 

 that we might get a pure and simple mode of vibration from them. 

 It is possible, but unlikely ; for atoms, even when isolated, have a 

 multitude of modes of vibration special to themselves, of which only 

 a few are of practical use to us, and we do not know how to excite 

 some without also the others. However, we do not at present deal 

 with individual atoms : we treat them crowded together in a com- 

 pact mass, so that their modes of vibration are really infinite. 



'■ We take a lump of matter, say a carbon filament or a piece of 

 quicklime, and by raising its temperature we impress upon its 

 atoms higher and higher modes of vibration, not transmuting the 

 lower into the higher, but superimposing the higher upon the lower, 

 until at length we get such rates of vibration as our retina is con- 

 structed for, and we are satisfied. We want a small range of rapid 

 vibrations, and we know no better than to make the whole series 

 leading up to them. It is as though, in order to sound some little 

 shrill octave of pipes in an organ, we were obliged to depress every 

 key and every pedal, and to blow a young hurricane. 



■' I have purposely selected as examples the more perfect methods 

 of obtaining artificial light, wherein the waste radiation is only use- 

 less, and not "noxious. But the old-fashioned plan was cruder even 

 than this: it consisted simply in setting something burning, whereby 

 not only the fuel, but the air, was consumed ; whereby also a most 

 powerful radiation was produced, in the waste waves of which we 

 were content to sit stewing, for the sake of the minute, almost in- 

 finitesimal fraction of it which enabled us to see. 



" E very one knows now, however, that combustion is not a pleas- 



ant or healthy mode of obtaining light ; but everybody does not 

 realize that neither is incandescence a satisfactory and unwasteful 

 method, which is likely to be practised for more than a few decades, 

 or perhaps a century. 



" Look at the furnaces and boilers of a great steam-engine driv- 

 ing a group of dynamos, and estimate the energy expended ; and 

 then look at the incandescent filaments of the lamps excited by 

 them, and estimate how much of their radiated energy is of real 

 service to the eye. It will be as the energy of a pitch pipe to an 

 entire orchestra. 



■' It is not too much to say that a boy turning a handle could, if 

 his energy were properly directed, produce as much real light as is 

 produced by all this mass of mechanism and consumption of ma- 

 terial. 



" There might, perhaps, be something contrary to the laws of na- 

 ture in thus hoping to get and utilize some specific kind of radiation 

 without the rest ; but Lord Rayleigh has shown, in a short com- 

 munication to the British Association at York, that it is not so, 

 and therefoie we have a right to try to do it. 



" We do not yet know how it is true, but it is one of the things 

 we have got to learn. 



" Any one looking at a common glow-worm must be struck with 

 the fact that not by ordinary coinbustion, nor yet on the steam-en- 

 gine and dynamo principle, is that easy light produced. Very little 

 waste radiation is there from phosphorescent things in general. 

 Light of the kind able to affect the retina is distinctly emitted ; and 

 for this, for even a large supply of this, a modicum of energy suf-' 

 fices. 



" Solar radiation consists of waves of all sizes, it is true ; but 

 then solar radiation has innumerable things to do besides making 

 things visible. The whole of the energy is useful. In artificial 

 lighting nothing but light is desired : when heat is wanted, it is 

 best obtained separately by combustion. And so soon as we 

 clearly recognize that light is an electrical vibration, so soon shall 

 we begin to beat about for some mode of exciting and maintaining 

 an electrical vibration of any required degree of rapidity. When 

 this has been accomplished, the problem of artificial lighting will 

 have been solved." 



Energy absorbed by Different Lights. — Mr. Preece, in 

 his address before the British Association, gave some figures on 

 the energy required to produce a light of one-candle power from 

 different illuminants. 



One candle light maintained by tallow absorbs 124 Watts 



" " "^ " " wax absorbs 94 '* 



" " ** " " spenn absorbs 86 



** " '* " '' mineral oil absorbs 80 *' 



'■ " " *' ** vegetable oil absorbs 57 



" *' " " '* coal-gas absorbs 6& " 



'• " '* *' " cannel-gas absorbs 48 " 



*' " '■ '* *' electricity (glow) absorbs. ... 3 " 



" " •" " " electricity (arc) absorb-S 5 '* 



The relative amounts of heat given off may be estimated from 

 these figures, tallow candle giving off 24S times as much heat as 

 an arc-lamp for the same amount of illumination. As for the cost 

 of production (Mr. Preece evidently does not include distribution), 

 the following figures hold good in London. The cost of producing 

 one candle light for one thousand hours is : — 



s. <L 



Sperm candles 8 6 



-Gas I 3 



Oil (petroleum) o 8 



Electricity (glow) o g 



Electricity (arc) o i)( 



The Shallenberger Electric Meter. — Among the nu- 

 merous meters for electric currents that have been lately invented, 

 that of Mr. Shallenberger is deserving of attention, from its inge- 

 nuity and apparent accuracy. It consists of a flat ring of soft iron 

 mounted on an aluminium disk fi.xed on a spindle and surrounded 

 by two coils, one of which is connected, either directly or through 

 a small converter, with a circuit whose current is to be measured ; 

 the other of which is of an oval form closely surrounding the iron 

 ring, and is short-circuited on itself. The meter is intended to 

 measure alternating currents, and its action is briefly as follows. 

 The alternating current in the first coil induces currents in both the 



