24G ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



Thompson lias contrived a simple apparatus for showing 

 the field of magnetic force produced by parallel currents. A 

 plate of glass is perforated by two holes close together, which 

 are traversed by one and the same wire, so arranged that the 

 current traverses the parallel lengths in the same or in oppo- 

 site directions. If, now, the plate be held horizontally while 

 the current passes, and fine iron filings be sprinkled on the 

 plate, they arrange themselves in the well-known forms of 

 magnetic spectra. They may be readily fixed by gum or 

 shellac, so as to be preserved for lantern projection. 



Becqnerel lias published an extended memoir on magnetic 

 rotatory polarization. The results which he has obtained tend 

 to show that both the direct and reverse magnetic rotations 

 of the plane of polarization of light, as is the case in the phe- 

 nomena of magnetism and diamagnetism, have a common 

 origin, and are the manifestation of a general property of 

 bodies that of becoming magnetic. This property is pos- 

 sessed to a more or less considerable degree by various sub- 

 stances, and the effects which have been observed may be 

 regarded as due to a difference between the magnetic ac- 

 tion of the molecules of the bodies and that of the medi- 

 um which envelops them. 



2. Electromotors. 



Maxwell has sent to Nature a note which he has received 

 from Pirani,of Melbourne, describing an experiment in which 

 an electric current appears to be produced by the direct ac- 

 tion of gravity. A glass tube eighteen inches long is filled 

 with a saturated solution of enpric sulphate, its ends closed 

 by copper caps to which w T ires are attached, and the whole is 

 connected with a delicate Thomson galvanometer. When 

 the tube was held vertically a deflection of 200 divisions was 

 observed, which Mas reversed on reversing the tube. 



Gaiffe has described a new and convenient form of voltaic 

 cell, which appears to be an improvement on the Leclanche 

 battery. It consists of a cylinder of pressed carbon contain- 

 ing holes parallel to the axis, which are filled with manga- 

 nese peroxide in fragments, and of a rod of amalgamated zinc. 

 These are placed in a glass vessel which is filled with a twen- 

 ty-per-cent. solution of zinc chloride as neutral as possible. 

 In action the battery forms zinc oxide, which falls in powder 



