146 



Anniversary Meeting. 



[Nov. 30, 



which indicates the time by means of the changes of polarization of the 

 blue light of the sky in the direction of the pole, founded on the discove- 

 ries of Arago and Quetelet. 



In 1835 he communicated to the British Association a paper on the 

 Prismatic Analysis of the Electric Light, proving that the electric spark 

 from different metals presents for each a different spectrum, exhibiting a 

 definite series of lines, differing in position and colour from each other, 

 and thus enabling very small fragments of one metal to be distinguished 

 with certainty from all the others. This was a starting-point in a new 

 and fertile field of physical inquiry which has abundantly rewarded the 

 labours of subsequent investigators. 



But no series of his researches have shown 'more originality and inge- 

 nuity than those by which he succeeded in measuring the velocity of the 

 electric current and the duration of the spark. The principle of the ro- 

 tating mirror employed in these experiments, and by which he was 

 enabled to measure time to the millionth part of a second, admits of appli- 

 cation in ways so varied and important that it may be regarded as having 

 placed a new instrument of research in the hands of those employed in 

 delicate physical inquiries of this order. 



Scarcely less valuable are the instruments and processes which Sir Ch. 

 Wheatstone devised for determining the constants of a voltaic circuit, in- 

 cluding, among others, the rheostat and the differential resistance mea- 

 surer (or "Wheatstone's bridge, as it is usually called), which, in one or 

 other of its modifications, is become an indispensable means of measuring 

 the resistance of telegraphic wires and cables, as well as for determining- 

 electromotive forces. The description of these methods is contained in a 

 paper in the 1 Philosophical Transactions ' for 1843. 



But it is with the Electric Telegraph that the name of Sir C. Wheatstone 

 is in the public mind most completely identified ; and ever since the first 

 messages were transmitted along the Great Western Railway by insulated 

 copper wires enclosed in iron tubes, to the present day — when a network 

 of copper wires insulated by means of caoutchouc is suspended across our 

 public thoroughfares for the instantaneous transmission of intelligence, 

 not merely from one district to another in our large towns, but from one 

 continent and capital to another — Sir C. Wheatstone has not ceased to 

 contribute the most important aid towards perfecting the means of electro - 

 telegraphic communication. 



A bare enumeration of these various inventions would carry us beyond 

 our limits on the present occasion. In 1840 he devised a cable adapted 

 for transmitting intelligence under the sea ; and it is to him that we are 

 indebted for the Alphabetic Dial Telegraph working without any clock- 

 power, and in which a magneto-electric machine supplies the place of a 

 voltaic battery. These instruments were first used in the Paris and Ver- 

 sailles Railway in 1846. 



A more recent invention is his High-Speed Telegraph, in which the 



