SCIENCE. 



When lamp-black is exposed to the -action of the light 

 of the spectrum it is found to give a sonorous response 

 to all of its rays as far as the middle of the violet, and 

 perhaps beyond. The intensity of the sound, however, 

 varies remarkably in different parts of the spectrum. 

 Taking the rays successively from different parts, from 

 the violet towards the red, the sounds begin very feebly 

 and increase in intensity, reaching a maximum in the ul- 

 tra red. Beyond that point they suddenly cease. The 

 increase of intensity is very gradual, the decrease very 

 sudden. 



Other substances have been experimented with, and 

 while exhibiting similar properties, each has a range of its 

 own. Porous and fibrous substances give loud sounds. 

 Thus, common wool or worsted are found to be very 

 sonorous, but the sounds are obtained wholly from the 

 visible parts of the spectrum and have the maximum in- 

 tensity in the green. In all substances tried success has 

 resulted, but nearly all have a very short range. 



In experimenting with more homogeneous substances 

 of simpler constitution, still more definite results are 

 obtained. The rays of the spectrum are passed through 

 sulphuric ether. Outside of the ultra red is a very nar- 

 row band which cause sounds while the other parts 

 fail to produce them. Hydrogen peroxide gives sounds 

 at several places wholly within the visible parts of the 

 spectrum, and these places are found to coincide with 

 the positions of the known • absorption bands of that 

 substance. The same is found to be true of Nitrogen 

 Oxide and a solution of Ammonia, Sulphate of Copper, 

 and many other substances. The general law deduced is 

 that sounds are produced in any substance by the rays 

 which it absorbs. 



Thus a kind of spectrum analysis can be obtained 

 through the intermediation of sound. The principal 

 value of the spectrophone, Mr. Bell believes, will be 

 found in the investigation of absorption bands in the 

 ultra red part of the spectrum. 



Mr. William B. Taylor inquired whether the sounds 

 observed from the two absorption bands of ammonia, 

 sulphate of copper, were octaves. Mr. Bell replied that 

 this question had not as yet been investigated. 



Mr. G. Brown Goode read portions of a paper on the 

 sword-fish and its allies, which paper will be published 

 in full in the next annual report of the U. S. Fish Com- 

 mission. 



ON THE MODERN DEVELOPMENT OF FARA- 

 DAY'S CONCEPTION OF ELECTRICITY.* 



By Professor Helmholtz. 



The majority of Faraday's own researches were con- 

 nected, directly or indirectly, with questions regarding 

 the nature of electricity, and his most important and most 

 renowned discoveries lay in this field. The facts which 

 he has found are universally known. Nevertheless, the 

 fundamental conceptions by which Faraday has been led 

 to these much-admired discoveries have not been re- 

 ceived with much consideration. His principal aim was 

 to express in his new conceptions only facts, with the 

 least possible use of hypothe:ical substances and forces. 

 This was really a progress in general scientific method, 

 destined to purify science from the last remnants of meta- 

 physics. Now that the mathematical interpretations of 

 Faraday's conceptions regarding the nature of electric 

 and magnetic force has been given by Clerk Maxwell, we 

 see how great a degree of exactness and precision was 

 really hidden behind his words, which to his contempor- 

 aries appeared so vague or obscure ; and it is astonishing 

 in the highest to see what a large number of general 



* The Faraday Ltctur.:, deliv.'re 1 bjfore ths Fellows of the- Chemical 

 So:icty in the Th : ure of th: k >y.il [mtitutiin, on Tius J ly, April 5th, 

 i8Ji,b/ PraieMOr HeloiholU. Ab;tra;i r.'vis:: 1 iy th: a'l.'io.-. 



theories the methodical deduction of which requires the 

 highest powers of mathematical analysis, he has found by 

 a kind of intuition, with the security of instinct, without 

 the help of a single mathematical formula. 



The electrical researches of Faraday, although embrac- 

 ing a great number of apparently minute and discon- 

 nected questions, all of which he has treated with the 

 same careful attention and conscientiousness, are really 

 always aiming at two fundamental problems of natural 

 philosophy, the one more regarding the nature of physi- 

 cal forces, or of forces working at a distance ; the other, 

 in the same way, regarding chemical forces, or those 

 which act from molecule to molecule, and the relation 

 between these and the first. 



The great fundamental problem which Faraday called 

 up anew for discussion was the existence of forces work- 

 ing directly at a distance without any intervening medium. 

 During the last and the beginning of the present century 

 the model after the likeness of which nearly all physical 

 theories had been formed was the force of gravitation 

 acting between the sun, the planets, and their satellites. 

 It is known how, with much caution and even reluctance, 

 Sir Isaac Newton himself proposed his grand hypothesis, 

 which was destined to become the first great and im- 

 posing example, illustrating the power of true scientific 

 method. 



But then came Oerstedt's discovery of the motions of 

 magnets under the influence of electric currents. The 

 force acting in these phenemena had a new and very 

 singular character. It seemed as if it would drive a 

 single isolated pole of a magnet in a circle around the 

 wire conducting the current, on and on without end, never 

 coming to rest. Faraday saw that a motion of this kind 

 could not be produced by any force of attraction or re- 

 pulsion, working from point to point. If the current is 

 able to increase the velocity of the magnet, the magnet 

 must react on the current. So he made the experiment, 

 and discovered induced currents ; he traced them out 

 through all the various conditions under which they 

 ought to appear. He concluded that somewhere in a 

 part of the space traversed by magnetic force there exists 

 a peculiar state of tension, and that every change of this 

 tension produces electromotive force. This unknown 

 hypothetical state he called provisionally the electrotonic 

 state, and he was occupied for years and years in find- 

 ing out what was this electrotonic state. He discovered 

 atfirst, in 1838, the dielectric polarisation of electric in- 

 sulators, subject to electric forces. Such bodies show, 

 under the influence of electric forces, phenomena per- 

 fectly analogous to those exhibited by soft iron under the 

 influence of the magnetic force. Eleven years later, in 

 1849, he was able to demonstrate that all ponderable mat- 

 ter is magnetized under the influence of sufficiently in- 

 tense magnetic force, and at the same time he discovered 

 the phenomena of diamagnetism, which indicated that 

 even space, devoid of all ponderable matter, is magnet- 

 izable ; and now with quite a wonderful sagacity and in- 

 tellectual precision Faraday performed in his brain the 

 work of a great mathematician without using a single 

 mathematical formula. He saw with his mind's eye that 

 by these systems of tensions and pressures produced by 

 the dielectric and magnetic polarisation of space which 

 surrounds electrified bodies, magnets or wires conducting 

 electric currents, all the phenomena of electro-static, 

 magnetic, electro-magnetic attraction, repulsion, and in- 

 duction could be explained, without referring at all to 

 forces acting directly at a distance. This was the part of 

 his path where so few could follow him ; perhaps a Clerk 

 Maxwell, a second man of the same power and independ- 

 ence of intellect, was necessary to reconstruct in the nor- 

 mal methods of science the great building, the plan of 

 which Faraday had conceived in his mind and attempted 

 to make visible to his contemporaries. 



Nevertheless the adherents of direct action at a dis- 

 tance have not yet ceased to search for solutions of the 



