S REPORT- -1884. 



scientific electricity. Just as in former days the science received a 

 stimulus from the application to telegraphy, under which everything 

 relating to measurement on a small scale acquired an importance and 

 development for which we might otherwise have had long to wait, so 

 now the requirements of electric lighting are giviDg rise to a new deve- 

 lopment of the art of measurement upon a large scale, which cannot 

 fail to prove of scientific as well as practical importance. Mere change 

 of scale may not at first appear a very important matter, but it is sur- 

 prising how much modification it entails in the instruments, and in the 

 processes of measurement. For instance, the resistance coils on which 

 the electrician relies in dealing with currents whose maximum is a 

 fraction of an ampere, fail altogether when it becomes a question of 

 hundreds, not to say thousands, of amperes. 



The powerful currents, which are now at command, constitute almost 

 a new weapon in the hands of the physicist. Effects, which in old days 

 were rare and difficult of observation, may now be produced at will 

 on the most conspicuous scale. Consider for a moment Faraday's great 

 discovery of the ' Magnetisation of Light,' which Tyndall likens to the 

 Weisshorn among mountains, as high, beautiful, and alone. This judg- 

 ment (in which I fully concur) relates to the scientific aspect of the 

 discovery, for to the eye of sense nothing could have been more insignifi- 

 cant. It is even possible that it might have eluded altogether the pene- 

 tration of Faraday, had he not been provided with a special quality of 

 very heavy glass. At the present day these effects may be produced 

 upon a scale that would have delighted their discoverer, a rotation of the 

 plane of polarization through 180° being perfectly feasible. With the aid 

 of modern appliances, Kundt and Rontgen in Germany, and H. Becquerel 

 in France, have detected the rotation in gases and vapours, where, on 

 account of its extreme smallness, it had previously escaped notice. 



Again, the question of the magnetic saturation of iron has now an 

 importance entirely beyond what it possessed at the time of Joule's early 

 observations. Then it required special arrangements purposely contrived 

 to bring it into prominence. Now in every dynamo machine, the iron of 

 the field-magnets approaches a state of satui'ation, and the very elements 

 of an explanation of the action require us to take the fact into account. 

 It is indeed probable that a better knowledge of this subject might lead 

 to improvements in the design of these machines. 



Notwithstanding the important work of Rowland and Stoletow, the 

 whole theory of the behaviour of soft iron under varying magnetic con- 

 ditions is still somewhat obscure. Much may be hoped from the in- 

 duction balance of Hughes, by which the marvellous powers of the 

 telephone are applied to the discrimination of the properties of metals, as 

 regards magnetism and electric conductivity. 



The introduction of powerful alternate-current machines by Siemens, 

 Gordon, Ferranti, and others, is likely also to have a salutary effect 



