10 



RKI'OIIT — 1884. 



measurement necessary to tlio completion of tlie system by taking 

 advantage of Faraday's law, that the quantity of metal decomposed 

 in an electrolytic coll is proportional to the whole quantity " elec- 

 tricity that passes. The best metal for the purpose is silver, deposited 

 from a solution of the nitrate or of the chlorate. The results recently 

 obtained by Professor Kohlrausch and by myself are in very good 

 agreement, and the conclusion that one ampei'c flowing for one hour 

 decomposes 4<"(>2o grains of silver, can liardly be in error by more than 

 a thousandth part. This number being known, the silver voltameter 

 gives fi ready and very accurate method of measuring currents of 

 intensity varying from -j',, ampere to four or live amperes. 



The beautiful and mysterious phenomena attending the discharge of 

 electricity in nearly vacuous spaces have been investigated and in some 

 degree explained by T)e La Hue, Crookes, Schcister, Moulton, and the 

 lamented Spottiswoode, as well as by various able foreign experimenters. 

 In a recent research Crookes has sous'ht the origin of a brij'ht citron- 

 coloured band in the phosphorescent spectrum of certain earths, and 

 after encountering difficulties and anomalies of a most bewildering kind, 

 has succeeded in proving that it is due to yttrium, an element muck 

 more widely distributed than had been supposed. A conclusion like thi» 

 is stated in a few words, but those only who have undergone similar ex- 

 perience are likely to appreciate the skill and perseverance of which it is 

 the final reward. 



A remarkable observation by Hall of Baltimore, from which it 

 appeared that the flow of electricity in a conducting sheet was disturbed 

 by magnetic force, has been the subject of much discussion. Mr. 

 Shelford Bidwell has brought forward experiments tending to prove 

 that the effect is of a secondary character, due in the first instance to the 

 mechanical force operating upon the conductor of an electric current when 

 situated in a powerful magnetic field. Mr. Bidwell's view agrees in the 

 main with Mr. Hall's division of the metals into two groups according to 

 the direction of the effect. 



Without doubt the most important achievement of the older genera- 

 tion of scientific men has been the establishment and application of the 

 great laws of Thermo-dynamics, or, as it is often called, the Mechanical 

 Theory of Heat. The first law, which asserts that heat and mechanical 

 work can be transformed one into the other at a certain fixed rate, 

 is now well understood by every student of physics, and the number 

 expressing the mechanical equivalent of heat resulting from the experi- 

 ments of Joule, has been confirmed by the researches of others, and 

 especially of Rowland. But the second law, which practically is even 

 more important than the first, is only now beginning to receive the full 

 appreciation due to it. One reason of this may be found in a not un- 

 natural confusion of ideas. Words do not always lend themselves readily 



