Feb. 17, 1 881] 



NA TURE 



367 



producing, at any given rate of rotation, the separate 

 tones of a common chord in succession : or by interpos- 

 ing a cylindrical lens to distribute the rays in a linear 

 beam to the four series at once, the united tones of the 

 chord could be produced simultaneously. 



Further it was found that the thickness and the breadth 

 of the receiving-disk makes no difference within certain 

 limits in the loudness or quality of the resulting tone. 

 And in the case of transparent substances such as mica 

 and glass these limits may be wide : in the case of glass 

 the loudness was the same with a disk of half a millimetre 

 as with one of three centimetres thickness. In conse- 

 quence rire substances miy be used in disks as small as 

 one square centimetre in area. Cracked or split disks of 

 glass, copper, and aluminium produce sensibly the same 

 effects as if they were whole. 



II. The molecular structure and state of aggregation of 

 the receiving disk appear to exercise no important influ- 

 ence upon the nature of the tones emitted. — Disks of 

 similar thickness and surface emit sounds of the same 

 pitch no matter of what material they be. Although there 

 may be slight specific differences between the actual 

 modes of production of the phenomenon from very thin 

 disks of different materials, these differences are reduced 

 to a vanishing quantity by rendering the receptive surface 

 alike, as for example by covering them all alike with a 

 film of lampblack. Moreover the effect produced by 

 ordinary radiations is, catcris paribus, the same practically 

 for transparent substances as widely differing from one 

 another as glass, mica, selenite, Iceland-spar, and quartz, 

 whether cut parallel or perpendicular to the optic axis, 

 and is the same in polarised light as in ordinary light. 



III. Tlie radiophonic sounds result from a direct action 

 of radiations upon the receiving substances. — This proposi- 

 tion appears to be established by the following facts : — 

 I . That the loudness of the sounds is directly proportional 

 to the quantity of rays that fall upon the disk. 2. That 

 by using a polarised beam and taking as a receiving-disk 

 a thin slice of some substance which can itself polarise or 

 analyse light, such as a slice of tourmaline, the resulting 

 sounds exhibit variations of loudness corresponding to 

 those of the rays themselves, when either polariser or 

 analyser is turned ; and the sound is loudest when the 

 light transmitted by the analysing disk is a minimum. 



IV. The phenomenon appears to be chiefly due to an 

 action on the surface of the receiver. — The loudness of the 

 emitted sound depends very greatly upon the nature of 

 the surface. Everything that tends to diminish the 

 reflecting power, and increase the absorbing power of 

 the surface, assists the production of the phenomenon. 

 Surfaces that are rough-ground or tarnished with a film 

 of oxidation are therefore preferable. It is also advan- 

 tageous to cover the receiving surface with black pul- 

 verulent deposits, bitumen black, platinum black, or 

 best of all with lampblack ; but the increase of sensi- 

 tiveness under this treatment is only considerable in the 

 case of very thin disks, as for instance from 'i to '2 of a 

 millimetre. Very sensitive radiophonic receivers may be 

 thus made with extremely thin disks of zinc, glass, or 

 mica smoked at the surface. It may here be noted 

 amongst M. Mercadier's results that for opaque disks, the 

 thinner they are the louder is the sound, and that 

 excellent results are given by metallic foil — copper, 

 aluminium, platinum, and especially zinc — of but 'Oj 

 millim thickness. The employment of such sensitive 

 receivers has enabled M. Mercadier to arrive at several 

 other important conclusions 



V. Radiophonic effects are relatively very intense. — 

 They can be produced not merely with sunlight or 

 electric light, but with the lime-light, and also with gas- 

 light, and even with petroleum flames, and with a spiral 

 of platinum wire heated in the Bunsen-flarae. 



VI . Radiophonic effects appear to be produced principally 

 by radiations of great wave-length, or those commonly 



regarded as calorifc.^Xn order to satisfy himself on this 

 point M. Mercadier had recourse to the spectrum direct, 

 without attempting to employ cells of absorbant material 

 such as alum solution or iodine in dissolved bisulphide of 

 carbon as ray-filters. A brilliant beam of light was pro- 

 duced by means of a battery of fifty Bunsen cells, and 

 with this, by means of ordinary lenses and a prism of 

 glass a spectrum was produced, the various regions of 

 which could be explored with one of the sensitive 

 receiving-disks mentioned above. The ma.ximum effect 

 was found to be produced by the red rays and by the 

 invisible ultra-red rays. From yellow up to violet, and 

 beyond, no perceptible results were obtained. The 

 e.xperiment was tried several times with receivers of 

 smoked glass, platinised platinum, and plain bare zinc. 

 The greatest effect appeared to be yielded at the limit of 

 the visible red rays. The rays which affect the electric 

 conductivity of selenium in the photophone are, as Prof. 

 W. G. .^dams has shown, not the red rays, but rays from 

 the yellow and green-yellow regions of the spectrum. 

 This fact alone would justify the distinction drawn 

 between the phenomena of radiophony and those of the 

 selenium photophone, though probably these are only two 

 of several ways of arriving at a solution of the problem 

 of the transmission of sonorous vibrations by radiation. 

 Theoretically a telephone with a blackened disk inclosed 

 in a high vacuum and connected with an external tele- 

 phone should serve as a receiver ; and the writer of these 

 lines has already attempted to devise a thermo-electric 

 receiver for reproducing sounds from invisible calorific 

 rays. S. P. T. 



THE JOHN DUNCAN FUND 



THE following subscriptions to this fund have been 

 received during the past week : — 



£ s. d. £ s.-d. 



Major Deedes ... o 10 o 



Anon 013 



Sir J. Fayrer I I o 



T. C. Kent 100 



Lavvson Tait I I o 



Heinrich Simon ...200 



Amount previously 



announced 4S 



Charles F. Tomes, 



F.R.S I 



J. S 2 



Dr. Vacher i 



K. R. Glover I 



Thomas Walker ... 5 



M. M. Pattison Muir I 



65 2 3 



THE TIME OF DA V IN PARIS 



THE importance of precise and uniform time through- 

 out Paris becoming ever and continually more 

 appreciated, the Municipality have taken the matter in 

 hand, and have established a system of what they call 

 " horary centres." These horary centres really consist of 

 standard clocks, erected in different places, and controlled 

 by electricity from the Paris Observatory. Moreover 

 each standard clock is furnished with additional electrical 

 work of its own, which enables it to send out an hourlv 

 current and control other clocks in its neighbourhood, 

 placed in circuit with it. The advantage of this arrange- 

 ment over any system of electrical dials is apparent, for 

 with the latter any mischance or practical joke with 

 the wires would cause the whole city to be misled or 

 completely deprived of time. The problem, as put by 

 Leverrier, and as it has been practically solved by M. 

 Breguet, was this :— To keep correct the hour given by 

 various regulators distributed in the city by means of an 

 electric current sent from the Observatory. If the current, 

 in consequence of any accident, fails, ihe regulators con- 

 tinue to work, with a very slight advance, without the 

 electric correction. The wires have their centre at the 

 Observatory, where there is an astronomical regulator 

 on the first floor. This instrument is maintained at 

 the exact time indicated by the astronomical observations, 



