264 A. M. Mayer on fixing and exhibiting Magnetic Spectra. 



have the researches of Faraday and W. Thomson on " tlie : 

 netic field '' and on " the lines of magnetic force " given to t 

 spectra— even when merely regarded as conventional syml" 

 an importance which has been fully shown; especially 

 Faraday, who was guided by their consideration to some v: 

 his most important discoveries. They have thus risen to so 

 high a theoretical importance that a method which will fix 

 them without danger of distortion, photographically reproduce 

 them and readily serve to exhibit them to the largest audi- 

 ences, will, I imagine, be acceptable to both investigators ami 



The only process of fixing these spectra, known to me, is 

 that practiced by De Haldat and Faraday, which, however, :~ 

 but an application to the magnetic spectra of the method 

 viously invented by Savart for preserving the Chladni ti^ 

 of vibrating plates. In this ^ ' ~^" 



the usual manner either on g] 

 upon them a sheet of paper coated with mucilage, to which im 

 filings adhere. In this operation of the transfer many particles 

 are deranged from their positions and the figures are yet more 

 distorted by the shrinkage of the wet paper, and are there- 

 fore not fit to serve in measures of precision; while the im- 

 pressions cannot be exhibited with much more facility than 

 the originals. 



My process is as follows : a clean plate of thin glass is coatea 

 with a firm film of shellac, by flowing over it a solution of tin? 

 substance in alcohol,* in the same manner as a photograpmc 

 plate is coated with collodion. After the plate has remained a 

 day or two in a dry atmosphere, it is placed over the magnet. 

 or magnets, with its ends resting on slips of wood, so that the 

 under surface of the plate just touches the magnet Fine no. - 

 filings, produced by *' draw-filing" Norway iron, wlueii 

 been repeatedly annealed, are now sifted uniformly ov- 

 film of lac by means of a fine sieve. The spectrum is tlu:; 

 duced on vibrating the plate, by letting fall vertically uj» 

 at different points, a light piece of copper wire. The ph^j^ ^ 

 now cautiously lifted vertically off the magnet and placed ^^ 

 the end of a cylinder of pasteboard, which serves as a suppo" 

 in bringing it quite close to the under surface of a cast-iio 

 plate (1 ft. diam. ^ in. thick), which has been heated ojer 

 large Bunsen-flame. Thus the shellac is uniformly heated anu 

 the iron-filings, absorbing the radiation, sink into the soften 

 film and are "fixed." e 



I generally allow the heat to act until the metalUc lustre o 

 the filings has disappeared, by sinking into the shellac, ana 



* Tlie shellac dissolved in strong alcohol is allowed to stand a week or mo 



