1867.] Physics. 133 



of contact-breaker introduced by Mr. Ladd, whicb allows the iron 

 to attain to the maximum of magnetization before the current ceases. 

 The static effects of the secondary current are also largely in- 

 creased by the use of a condenser, as suggested by M. Fizeau, 

 although the principle of its action is by no means clearly under- 

 stood. Dr. Noad's ' Inductorium ' gives a complete description 

 and explanation of these instruments, together with a number of 

 scientific and popular experiments which may be made with them. 

 The ' Small Induction Coil '* by J. H. is a description of the 

 cheaper forms of coils which have lately become so popular. 

 Without attempting an explanation of their principles, the author 

 contents himself with showing their construction, and the purposes 

 to which they may be applied ; and, for the majority of purchasers 

 of these instruments, his pamphlet will, we think, be found 

 sufficient. 



Some yeij valuable researches on the propagation of electricity 

 in highly-rarefied elastic fluids, and on the stratifications of the 

 electric light which accompany this propagation, have been 

 published by M. A. De la Bive. The author has introduced a 

 novel method of research, which appears capable of throwing 

 considerable light on these obscure phenomena. He takes a large 

 glass globe, furnished with four tubulures, having leather stuffing- 

 boxes traversed with metallic rods. Two of these are connected 

 with a powerful Bunsen's battery, and the voltaic arc is produced 

 between them. The other two rods are intended for the passage of 

 an electric current from an induction coil. The voltaic arc is simply 

 used as a source of heat to fill the exhausted globe with metallic 

 vapours, and the phenomena which the author has investigated, are 

 those produced by the passage of the induction current through 

 this metallic vapour. The globe is first well exhausted, and then 

 rilled with nitrogen, which is rarefied to tw T o or three millimetres' 

 pressure, the induction-current is then turned on, and the Bunsen's 

 battery is connected with the other rods, so as to produce a voltaic 

 arc. In a few minutes the intensity of the induction- current aug- 

 ments considerably, and its colour alters according to the nature 

 of the points between which the voltaic arc is formed. With 

 points of silver or zinc the light is of a decided blue colour; 

 with copper, the tint is very deep green; with cadmium, 

 apple-green ; with magnesium, fight green ; and with aluminium, 

 greenish white. In a second part of the paper the author studies 

 the stratifications of the electric light, which he considers to be 

 a phenomenon analogous to the production of sonorous waves. 

 The third part is devoted to a discussion of particular phenomena 



* 'A Popular Description of the Small Induction Coil, with a Variety of very 

 Beautiful and Instructive Experiments.' By J. H. London : Varty Sz Cox. 



