Nov. 29, 1888] 



NATURE 



107 



ipitulate the principal physical conclusions which 



to be legitimately deducible from the whole in- 



jation ; in this recapitulation qualifications must 



jssarily be omitted or stated with great brevity. 



[When two meteorites are in collision, they are virtually 



fhly elastic, although ordinary elasticity must be nearly 



)perative. 



]K swarm of meteorites is analogous with a gas, and 



laws governing gases may be applied to the discussion 



its mechanical properties. This is true of the swarm 



which the sun was formed, when it extended beyond 



orbit of the planet Neptune. 



Vhen the swarm was very widely dispersed, the arrange- 

 it of density and of velocity of agitation of the 

 Iteorites was that of an isothermal-adiabatic sphere. 

 I Iter in its history, when the swarm had contracted, it 

 is probably throughout in convective equilibrium. 

 The actual mean velocity of the meteorites is determin- 

 able in a swarm of given mass, when expanded to a given 

 extent. 



The total energy of agitation in an isothermal-adiabatic 



here is half the potential energy lost in the concentration 



om a condition of infinite dispersion. 



The half of the potential energy lost, which does not 



reappear as kinetic energy of agitation, is expended in 



volatilizing solid matter, and heating the gases produced 



■on the impact of meteorites. The heat so generated is 



gradually lost by radiation. 



The amount of heat generated per unit time and volume 

 varies as the square of the quasi-hydrostatic pressure, and 

 inversely as the mean velocity of agitation. The tem- 

 perature of the gases volatilized probably varies by some 

 law of the same nature. 



The path of a meteorite is approximately straight, 

 except when abruptly deflected by a collision with another. 

 This ceases to be true at the outskirts of the swarm, 

 where the collisions have become rare. The meteorites 

 here describe orbits under gravity which are approximately 

 elliptic, parabolic, and hyperbolic. 



In this fringe to the swarm the distribution of density 

 ceases to be that of a gas under gravity ; and as we 

 recede from the centre the density at first decreases more 

 rapidly, and afterwards less rapidly than if the medium 

 were a ga?. 



Throughout all the stages of its history there is a sort 

 of evaporation by which the swarm very slowly loses in 

 mass, but this loss is more or less counterbalanced by 

 condensation. In the early stages the gain by condensa- 

 tion outbalances the loss by evaporation ; they then equili- 

 brate, and finally the evaporation may be greater than 

 condensation. 



Throughout the swarm the various meteorites are to 

 some extent sorted according to size ; as we recede from 

 the centre the number of small ones preponderates more 

 and more, and thus the me.ui mass contiaually diminishes 

 with increasing distance. The loss by evaporation falls 

 principally on the small meteorites. 



A meteor swarm is subject to gaseous viscosity, which 

 !s greater the more widely diffused is the swarm. In 

 consequence of this a widely extended swarm, if in rotation, 

 will revolve like a rigid body without relative motion 1 

 (other than agitation) of its parts. 



Later in the history the viscosity will probably not | 

 suffice to secure uniformity of rotation, and the central 

 portion will revolve more rapidly than the outside. ' 



The kinetic theory of meteorites may be held to pre- \ 

 sent a fair approximation to the truth in the earlier stages I 

 of the evolution of the system. But later, the majority of 

 the meteors will have been absorbed by the central sun , 

 and its attendant planets, and amongst the meteors which 

 remain free the relative motion of agitation must have 

 been largely diminished. These free meteorites— the 

 dust and refuse of the system— probably move in clouds, 

 but with so little remaining motion of agitation that 



(except perhaps near the perihelion of very eccentric 

 orbits) it would scarcely be permissible to treat the cloud 

 as in any respect possessing the mechanical properties of 

 a gas. 



The value of this whole investigation will appear very 

 different to different minds. To some it will stand con- 

 demned as altogether too speculative ; others may think 

 that it is better to risk error in the chance of winning 

 truth. To me, at least, it appears that this line of thought 

 flows in a true channel ; that it may help to give a mean- 

 ing to the observations of the spectroscopist ; and that 

 many interesting problems, here barely alluded to, may 

 perhaps be solved with sufficient completeness to throw 

 light on the evolution of nebulas and planetary systems. 



EDISON'S PERFECTED PHONOGRAPH. 



nPHE marvellous results attained by Mr. Edison's 

 •*■ recent improvement on, or, more properly perhaps, 

 resurrection of, the original phonograph of 1878 have 

 induced us to present a view of the latest form of the 

 instrument, together with a short description of its main 

 features and most recent performances. 



Mr. Edison is still occupied in perfecting the instru- 

 ment, and scarcely a week passes without his sending 

 over to his European colleague, Colonel Gouraud, sub- 

 stantial evidences of progress towards perfecting the 

 arrangements either for the recording and reproducing 

 of all kinds of sounds, or else in the construction and 

 the postal conveyance of phonograms. 



Although, therefore, the instrument can hardly at pre- 

 sent be said to have reached its final stage of develop- 

 ment, in its chief constructive points it may be regarded 

 as practically perfected ; while some recent trials of it 

 show that it is capable not merely of recording, but of repro- 

 ducing, every kind of sound with which we are acquainted, 

 including articulate speech, with a fidelity little short of 

 absolute perfection. 



When L^on Scott invented his phonautograph, he 

 unconsciously came near the phonograph, though he 

 merely contented himself with reproducing the vibrations 

 pictorially on a blackened surface. Prof Helmholtz, on 

 the other hand, by his profound studies in the analysis 

 and synthesis of speech into fundamentals, accompanied 

 by varying combinations of subsidiary harmonics, seems 

 to have created quite a scare among the phonograph! sts, 

 by showing them what a terribly complicated affair arti- 

 culate speech was. In the phonograph, however, we have 

 a machine which not only differentiates all these com- 

 plicated systems of vibrations, checks, and harmonics, but 

 integrates them equally well. It is, moreover, capable of 

 repeating the integrations practically as often as we please. 



This perfected power of record, reproduction, and pre- 

 servation of sound has been accomplished partly through 

 the substitution of a specially prepared wax for the original 

 tinfoil, but also a good deal tlifough other improvements 

 in the diaphragms, needles, &c. The vibrations of the 

 recording diaphragm are transferred by means of a 

 cutting-needle to the wax, which is thus carved and 

 indented into a series of hills and valleys, which represent 

 in intaglio the resultant form of the original sound- vibra- 

 tions, including part, if not all, of the minor inflections due 

 to the presence of the subsidiary harmonics or overtones. 



The tinfoil used in the original machine of 1878 only 

 very partially fulfilled the office of a recording surface, 

 and since every indentation in it necessarily involved a 

 corresponding rise of the material on either side, the 

 vibrations of the recording style, and a fortiori of the air 

 itself, were only very imperfectly reproduced on its surface. 

 The hollow character of the undulations, moreover, caused 

 them to be easily effaced after a few repetitions. 



The records on the wax, on the other hand, have been 

 recently reproduced over 3000 times. 



