C. ELECTRICITY, LIGHT, HEAT, AND SOUND. 41 



C. ELECTRICITY, LIGHT, HEAT, AND SOUND. 



PHOTOGRAPHING MAGNETIC CURVES. 



Professor A. M. Mayer, of Lehigh University, has devised 

 an ingenious method of fixing, photographing, aifd exhibiting 

 the magnetic spectra. For this purpose he takes a clean 

 plate of thin glass and coats it with a film of shellac, formed 

 by flowing over it an alcoholic solution of this substance just 

 as the photographic print is coated with collodion. After 

 the plate has remained a day or two in a dry atmosphere, it 

 is placed over a magnet or magnets, with the ends resting on 

 slips of wood so that, the under surface of the plate just 

 touches the niasmet. Fine iron filings are now sifted uni- 

 formly over the film of lac by means of a fine sieve. The 

 spectrum is then produced, on vibrating the plate, by letting 

 fall vertically upon it, at different points, a light piece of 

 copper wire. The plate is now cautiously lifted off the mag- 

 net, and brought quite close to the under surface of a cast- 

 iron plate which has been well heated. Here the shellac is 

 softened uniformly, and the iron filings sink into the film, and 

 are fixed. The heat should be allowed to continue until the 

 metallic lustre of the filings has disappeared by sinking into 

 the shellac, and the film appears quite transparent. After 

 the plate is cooled, any superfluous filings are knocked off by 

 inverting and gently tapping it. These plates may then be 

 used either as permanent objects of exhibition, or as nega- 

 tives from which to print, in the usual way, an accurate rep- 

 resentation of the foci, lines of direction, etc. They can also 

 be used as slides for a magic lantern. Am. Jour. &ci., April, 

 1871,260. 



duchemin's electric pile. 



M. Duchemin has recently presented to the notice of the 

 French Academy of Science a new electrical pile, which is 

 so arranged that, on being placed in contact with the sea, it 

 instantly becomes a source of electricity, by means of the 

 oxidizing of the liquid which surrounds it, as well as by agi- 

 tation and perpetual renewal. His model consisted of a per- 



