April 2"], 1876] 



NATURE 



503 



To remove this difficulty, Wheatstone invented a very 

 ingenious apparatus, by which the vibratory motions of 

 the luminiferous ether could be represented with consider- 

 able fidelity, and especially the phenomena of polarisa- 

 tion, whether rectilinear, circular, or elliptic. 



Many were the achievements realised by Wheatstone 

 in applying himself to optics : we owe to him the inven- 

 tion of a kaleidoscope, in which the persistence of im- 

 pressions on the retina was utilised in demonstrating the 

 transversal vibrations of an elastic rod fixed at one of its 

 extremities ; we owe to him one of the most sensitive 

 photometers, as also the way of estimating the duration of 

 lamps, the movements of the sea, and the ramifications of 

 the retina; the difference between the solar and the electric 

 light, and the lines of the light obtained from combustion 

 of bodies brought to the poles of the voltaic battery. He 

 was, further, the inventor of the polar clock, an instru- 

 ment designed to indicate the hours through observation 

 of the plane of polarisation of light of the blue sky in the 

 region of the North Pole. That instrument, improved by 

 Soleil, was marvellously adapted for finding the neutral 

 points of Arago, Babinet, and Brewster. 



The science of acoustics also profited by the valuable 

 researches of our Lincean correspondent, for he experi- 

 mented on sound and on hearing, devised his kaleido- 

 phone, occupied himself with resonance or reciprocal 

 vibrations produced by a column of air ; he also studied 

 the transmission of musical sounds, and the figures ob- 

 tained with sand on a vibrating surface, or acoustic 

 figures. 



Moreover, he cultivated, with great advantage to science, 

 electro-dynamics ; and devised two rheostats, one for great, 

 the other for small resistances. 



We are indebted to the illustrious deceased for many 

 other scientific contributions, which have realised a 

 notable progress in various branches of modern physics, 

 and especially in telegraphy. Among these contributions, 

 which time would fail fully to enumerate, we must not 

 omit to speak of the method, so fruitful of valuable con- 

 sequences, by which Wheatstone determined the velocity 

 of the electric discharge in a metallic wire. 



He was likewise skilled and practised in ballistics ; and 

 he employed the uniform rotation of two pasteboard discs, 

 fixed on a common horizontal axis passing through their 

 centres, to ascertain the initial velocity of a projectile 

 fired from a gun. The projectile, traversing with uniform 

 velocity these rotating discs, produced within two holes 

 the diff"erent situations of which afforded a means of 

 determining the initial velocity of the ball. 



Wheatstone was the first to employ the rapid rotation of 

 a reflecting disc for measuring the velocity of propaga- 

 tion of an imponderable agent, without resorting to great 

 distances, such as the planetarj-. After having in vain 

 turned the spark-exciting organ round an axis, hoping to 

 be able to increase the extent of sparks, and also to alter 

 their direction, according to the direction of turning, he 

 conceived the idea of communicating to a reflecting disc 

 or plane mirror a very rapid rotatory action, by which the 

 electric spark produced at a certain distance from the 

 disc might be reflected. 



The interesting consequences derived from these expe- 

 riments are — (i) that electricity takes an appreciable time 

 in traversing a distance, whence may be inferred approxi- 



mately the velocity of the electric current ; (2) that this 

 velocity does not depend on the direction of the electric 

 current ; (3) that of three sparks, reflected by this means, 

 in the same horizontal direction, the two lateral ones 

 appear contemporaneously, but the middle appears re- 

 tarded with respect to the first, which fact is not recon- 

 cilable with the hypothesis of Franklin on the nature of 

 electricity ; (4) that the same method was adopted by the 

 celebrated Arago, whose experiments lead to a decisive 

 judgment which of the two theories on the nature of light, 

 that based on emanation, or that based on ethereal vibra- 

 tion, must prevaiL 



The fact that we now possess methods of determining 

 the velocity of light so practical, elegant, and speedy as 

 those of the distinguished physicists Fizeau and Foucault, 

 is due to the method of rotating mirrors, which was intro- 

 duced through this order of researches of the English 

 physicist, of whom we deplore being for ever bereaved ; 

 the fame of whose discoveries is everywhere — 



** And v/ith the world itself shall still endure," 



Dante, Inf., ii. v. 60. 

 P, VOLPICELLI 



I THE PROGRESS OF THE LOAN COLLECTION 



VARIOUS are the trains of thought suggested by a 

 visit to those galleries in which the science of the 

 past and the present is being represented by so goodly 

 an array of its working implements. If one has been at 

 all in sympathy with the movement which is now so 

 near its goal (and who that has in the least appreciated 

 the progress and benefits of science can be out of 

 sympathy with it ?), it will, first of all, be truly gratifying 

 to him to observe on every hand such manifest tokens 

 of hearty co-operation in the movement. Even those 

 who are engaged in marshalling the various treasures 

 of the departments which have been entrusted to their 

 charge seem to be animated with an unusual zeal (a zeal 

 promising the best results), and, at first sight even, 

 it is evident that the various museums and private 

 collections in this country and on the Continent have 

 been ransacked for some of their choicest contents to be 

 sent to these South Kensington galleries, aiding the com- 

 pletion of an ideal which is true in its comprehensiveness. 

 The nations of the Continent who were appealed to for 

 their support of the scheme, have shown, many of them, 

 by an activity which is beyond all praise, how warmly the 

 proposal has been entertained. This is especially true of 

 Germany. The Berlin Committee appointed a short time 

 ago, and including some of the foremost names in science, 

 while it gained also the useful accession of Imperial 

 influence, promptly made application (the time was short) 

 to the various Universities and Polytechnic Schools 

 throughout the country, and they were met as promptly ; 

 so that soon quite a network of subordinate committees 

 came into being, all working harmoniously towards the com- 

 mon end. The German contributions form a very con- 

 siderable proportion of the whole ; and they, in common 

 with contributions from the Continent generally, are indeed 

 surprising in their extent, if we consider the shortness of 

 time allowed and the unique character of the exhibition. 

 Both Germans and French have been doing all that they 





