ADDBESS. 1 5 



Again, to enumerate a few more instances of the measurement of 

 minute quantities, there are the average distances of molecules from 

 one another in various gases and at various pressures ; the length of their 

 free path, or range open for their motion without coming into collision ; 

 there are movements causing the pressures and differences of pressure 

 under which Mr. Crookes' radiometers execute their wonderful revolutions. 

 There are the excursions of the air while transmitting notes of high pitch, 

 which through the researches of Lord Rayleigh appear to be of a diminu- 

 tiveness altogether unexpected. There are the molecular actions brought 

 into play in the remarkable experiments by Dr. Kerr, who has succeeded, 

 where even Faraday failed, in effecting a visible rotation of the plane of 

 polarisation of light in its passage through electrified dielectrics, and on 

 its reflexion at the surface of a magnet. To take one more instance, which 

 must be present to the minds of us all, there are the infinitesimal ripples 

 of the vibrating plate in Mr. Graham Bell's most marvellous invention. 

 Of the nodes and ventral segments in the plate of the telephone which 

 actually converts sound into electricity and electricity into sound, we can 

 at present form no conception. All that can now be said is that the most 

 perfect specimens of Chladni's sand figures on a vibrating plate, or of 

 Kundt's lycopodium heaps in a musical tube, or even Mr. Sedley Taylor's 

 more delicate vortices in the films of the Phoneidoscope, are rough and 

 sketchy compared with these. For notwithstanding the fact that in the 

 movements of the Telephone-plate we have actually in our hand the solu- 

 tion of that old world problem, the construction of a speaking machine ; 

 yet the characters in which that solution is expressed are too small for our 

 powers of decipherment. In movements such as these we seem to lose 

 sight of the distinction, or perhaps we have unconsciously passed the 

 boundary between massive and molecular motion. 



Through the Phonograph we have not only a transformation but a per- 

 manent and tangible record of the mechanism of speech. But the differ- 

 ences upon which articulation (apart from loudness, pitch, and quality) 

 depends, appear from the experiments of Fleeming Jenkin and of others 

 to be of microscopic size. The Microphone affords another instance of the 

 unexpected value of minute variations, — in this case of electric currents ; 

 and it is remarkable that the gist of the instrument seems to lie in obtain- 

 ing and perfecting that which electricians have hitherto most scrupulously 

 avoided, viz., loose contact. 



Once more, Mr. De La Rue has brought forward as one of the results 

 derived from his stupendous battery of 10,000 cells, strong evidence for 

 supposing that a voltaic discharge, even when apparently continuous, may 

 still be an intermittent phenomenon ; but all that is known of the period 

 of such intermittence is, that it must recur at exceedingly short intervals. 

 And in connexion with this subject, it may be added that, whatever be 

 the ultimate explanation of the strange stratification which the voltaic 

 discharge undergoes in rarefied gases, it is clear that the alternate disposi- 



