68 



POPULAE SCIEiirOE NEWS. 



[May, 1888. 



struction, to inform him that the members of the 

 Academy had organized a club, a free society, which 

 proposed to continue tlie Academy's work till the 

 Government had come to a decision concerning 

 its future. Lakanal approved of the plan, and 

 allowed the meeting to be held in the rooms of 

 the Academy ; but three days later the rooms 

 were shut. The Academy of Sciences was entirely 

 suppressed. 



Two years later, Bonaparte, then P'irst Consul, 

 reorganized the Academy somewhat after Colbert's 

 original but unexecuted plan. The different acad- 

 emies were incorporated in a single body, the In- 

 stitute of France. The Academy of Sciences 

 remained as it was, in itself. The meetings were 

 held in the same rooms ; the old members kept 

 their places and titles: but in 1801 the rooms of 

 the Louvre were deemed insufficient, and Bona- 

 parte decided to secure new lodgings for the In- 

 stitute. The Palais des Qua/re Nations was chosen : 

 it is the pre.sent seat of the In.stitute, where the 

 different academies meet turn in turn in different 

 rooms. That of the Academy of Sciences is a large 

 one ; rather dark, it must be said, but well furnished 

 and decorated. Up to 1875 it was lighted by can- 

 dles: gas has been used only since that time. It 

 was in 1879 that electric bells were for the first 

 time used in this temple of science. As to tele- 

 phones, no one thinks of them yet. This state of 

 things is rather ludicrous, and is well calculated to 

 excite the hilarity of outsiders, as it does in fact. 

 The members of the Academy of Sciences have 

 been paid a small sum from the beginning. Louis 

 XIV. had pensioned many of them, but the sums 

 paid to each were not the same. At present each 

 member receives three hundred dollars per year : 

 this sum was decided by Carnot, the grandfather 

 of the present President of the French Republic, 

 who was at that time (1796) president of the Di- 

 recioire. 



Although the different academies are of ancient 

 date, the Institute, which is the body consisting of 

 the five academies incorporated together, is one of 

 Bonaparte's creations. Bonaparte himself was a 

 member of the Academy of Sciences. He was 

 elected (1797) in the class of mechanics, in the 

 place of Carnot, who had been obliged to take a 

 refuge in foreign parts. It was also Bonaparte who 

 decided the uniform which is at present worn by 

 the members of the Institute in different official 

 circumstances ; who proposed to award a gold medal 

 to Volta, after reading his memoir on galvanism 

 and the galvanic fluid. He resigned his office in 

 1817, and his place had been occupied since by 

 Molard, Combes, Tresca; and Maral Desprez is the 

 present holder of this illustrious chair. 



We have not been able to condense in so short 

 a space many very interesting facts concerning the 

 history of this enlightened and illustrious scientific 

 corporation, but the principal dates of its history 

 have been recalled. Readers who are anxious to 

 know more should refer to M. Maindron's excel- 

 lent work, in which all the necessary documents 

 have been collected. H. 



THE DIFFRACTION OF SOUND. 



At a recent meeting of the Royal Institution a 

 lecture was delivered upon " The Diffraction of 

 Sound," by Lord Rayleigh. The lecturer said 

 that his subject had been furnished by the close 

 analogy existing between light and sound, both of 

 which are transmitted by undulatory vibrations. 

 He then proceeded to prove, by a series of delicate 

 experiments, that "sound-shadows" exist as well 

 as the shadow produced by light, although under 

 ordinary conditions they are not sufficiently sharp 

 and distinct to be very noticeable. This disa- 



greement, it was pointed out, is due to the great 

 difference existing between the comparative wave- 

 lengths of light and sound. Thus, in air the 

 wave-length of "middle C " in the musical scale 

 is about four feet, whilst the ray in the middle of 

 the spectrum has a wave-length of only one-forty- 

 thousandth of an inch, a proportion of about 1 to 

 2,000,000. Under favorable conditions, however, 

 "sound-shadows" are much more definite than 

 might be supposed. In his experiments the lecturer 

 chose as his source of sound a note extremely high 

 on the musical scale,- — so high, indeed, as to be 

 quite inaudible to the human ear. Since the mech- 

 anism of the ear would not, therefore, be sufficient- 

 ly sensitive to distinguish between the presence or 

 absence of this sound, a more delicate test had to be 

 devised. This difficulty was overcome by the lectur- 

 er through the introduction of a " sensitive flame." 



This flame was described as consisting of a jet of 

 gas driven at a great pressure through a minute 

 orifice; the pressure being so regulated, that the 

 flame, although burning quietly and steadily under 

 normal conditions, immediately began to flare upon 

 the interference caused by the vibratory motion 

 communicated to the atmosphere by the sound. 

 Under these conditions, even when the "sensitive 

 flame " and the source of sound were some twelve 

 feet apart, the lecturer was able to cause the flame 

 to burn quietly or to flare by the mere respective 

 introduction or withdrawal of his hand at any 

 po.sition between the flame and the source of sound. 



A further phase of this phenomenon was rendered 

 apparent when an obstruction, however slight, was 

 placed behind the flame, so as to reflect the sound 

 back along the path it had travelled. The lecturer 

 obtained by this means what he terms " stationary 

 waves," or waves of sound which have stationary 

 "nodes; " and " loops," that is, zones at which a 

 minimum or maximum amount of vibratory move- 

 ment respectively occur. ' By altering the distance 

 between the reflector and the " sensitive flame," he 

 showed that flarings of the flame, when it coincided 

 in position with the " loops," were contrasted with 

 quiet periods when " nodes " were reached. Since 

 the distance between a "node" and a "loop" 

 must evidently be equal to half the wave-length of 

 the note producing the disturbance. Lord Rayleigh 

 pointed out that the pitch of the note could easily 

 be calculated by using a reflector made to slide 

 along a scale. In this way he ascertained the note 

 he had employed in his experiments to possess a 

 wave-length of half an inch, and therefore to be 

 between six and seven octaves above " middle C." 

 Further, he remarked, that, as the " nodes " occur 

 at the place of minimum disturbance, it follows 

 that their distance from the source must be an even 

 multiple of the wave-length of the note; on the 

 contrary, the position of the " loops " would be 

 furnished by an odd multiple of the wave-length. 



Attention was then drawn to another remarkable 

 property of the " sensitive flame," — that although 

 the sound caused the flame, when placed in a cer- 

 tain position, to flare, no effect was produced when 

 the flame was revolved on its own axis, so as to be 

 at right angles to its former position. But the 

 flaring could be produced when in this position by 

 diverting the sound in a direction making an acute 

 angle with its former course, and then reflecting it 

 from a plane surface so that it reached the flame at 

 the same point as before its position was altered. 

 In this experiment, also, the lecturer showed the 

 existence of cycles of " nodes " and " loops " by 

 successively advancing and withdrawing the re- 

 flector to and from the " sensitive flame," although 

 maintaining the same relative position with the 

 source of sound. The concluding experiment was 

 still more interesting, in affording additional proof 

 of the correctness of the principles enunciated by 



Huygens respecting the undulatory transmission of 

 light. The lecturer directed the wave of sound 

 through an aperture about two feet wide, and so 

 adjusted the flame as to barely flare with the dis- 

 turbance. He then showed, that by placing an 

 obstacle so as to occupy either the space in the 

 centre half of the aperture, or the area of the encir- 

 cling external half, in both cases the intensity of 

 the effect was increased to such an extent as to 

 cause the flame to flare vigorously. The lecturer 

 proved, by reasoning analogous to that employed 

 in Huygens's Zones, that this phenomenon was 

 due to the " pencil " of sound being made up of 

 concentric rings of equal but opposite vibratory 

 intensity, producing in combination a nearly neu- 

 tral effect upon the flame. By interception of the 

 centre rings, the passage of the outer rings would 

 produce a greater aggregate effect upon the " sensi- 

 tive flame," since they would contain a preponder- 

 ance of one motion ; whilst the same effect would 

 be produced by the reversal of the conditions, since 

 a preponderance of the other motion would then 

 exist. In conclusion. Lord Rayleigh pointed out 

 the analogy existing between this theory and that 

 demonstrated by Fresnel regarding the formation 

 of a bright spot in the shadow produced by the 

 interception of the middle rays of a "pencil "of 

 light in a similar manner. — London Pharmaceuti- 

 cal Journal. 



SCIENTIFIC BREVITIES. 



One pound of mercury converted into fulminate 

 is sufficient to charge fifty thousand percussion 

 caps. 



In London recently an egg of the extinct great 

 auk {Alca impennis} was sold for two hundred and 

 twenty pounds. It belonged to the collection of 

 Mrs. Wise, whose husband bought it of a dealer in 

 Oxford Street in 1851 for eighteen pounds. It was 

 originally brought to England from Paris, and is 

 now said to have been bought for America. 



Prehistoric Altars. — There has recently been 

 discovered in the high Alps, near the summit of 

 the great St. Bernard, five large granite altars and 

 numerous other relics of the stone age, used in 

 pagan epochs for sacrifices. Swiss scientists con- 

 sider this discovery a proof that Mount St. Bernard 

 was a place of sacrifice in pagan times, and that 

 the canton of Valais must have been inhabited by 

 human beings as far back as the stone age. 



The Ancient Greeks. — Professor Trent of 

 Johns Hopkins University, lecturing to Baltimore 

 workingmen, has been impressing the fact that 

 there is nothing new under the sun. There were 

 tenement-houses, he says, in ancient Athens, with 

 many families in one house; there were corners 

 in the iron market and in the olive-oil industry 

 then, manipulated just as are Wall-street corners 

 now ; and there were slave-insurance offices, where 

 the old Greek, for about one dollar a year, could 

 be insured against his slaves running away. 



Dynamite is so instantaneous in its action, that 

 a green leaf can be compressed into the hardest 

 steel before it has time to flatten. One of the ex- 

 periments at the United States Torpedo Works was 

 to place some leaves between two heavy flat pieces 

 of iron, set them on a firm foundation, and see 

 what gun-cotton would do in forcing the iron pieces 

 together. A charge was placed upon them by com- 

 prestiiig the gun-cotton into a cylindrical form 

 about one inch thick and three or four inches in 

 diameter, through the centre of which a hole is 

 made for a cap of fulminate of mercury, by which 

 the gun-cotton is exploded. The reaction was so 

 great, from merely being exploded in the open air, 

 that one of the iron pieces was driven down upon 

 the other quick enough to catch an impression of 

 the leaves before they could escape. 



