.1. }L Mayer on fixing and exhibiting Magnetic Spectra. 2G5 



joars quite transparent. This degree of action is ner.. 

 Mtni photographic prints are to be made from the pluir 

 .I'll they are to be used as lantern slides I do not can, 

 :.ting so far. After the plate has cooled, it is allowed i- 



1 may be removed. 

 -!;(U-t experience will give the proper stnipjtli o| ^h.llac 

 '1! to obtain a film so thick as just t" l» sufii, „ i-j tn /,,..',/ tJ,v 

 '7\ ;iiid the requisite amount of heat to lii-mlv criiicnt tin •. . 

 v.. Hi. Hit iiijiirintr the transparency of the lilm. 



The i.lates <'au now serve (1) for the most arruraie inr;,- .; 

 ui'oii tlK' inagnetic-field; (2) for a photograj-lnc iH-suiw. -ah: 

 :iit' printing-frame will produce the lines in whitf niion a .!,.r 

 1. giving most beautiful and distinct ';iiijn\s>ion> ;'■' \'.\^^<\\ 

 ~ required to exhibit these figures lo an au<li(ii((. the 

 .•■re provided with glass covers, kept Imni toiulung the 

 ra by intervening sHps of card-boanl. and thrrc n-ult 

 .-'■'les, m every way fit for giving a line exhiMtion, whrii i!'' 

 miages are projected upon a screen. I liave thus <.l.tai!;.-: 

 images, clear and sharp, of over 12 feet in dianietii-.f 



By this process many plates have been proiluceil : sho>'. . 

 tlie action of single magnets of various fe^rnis, and ot juxt; . 

 sed bars ; as well as the effects of electric currents led l-y v, 

 through holes drilled in the plates. Those exhihiting ■ 

 inductive action of magnets on bars of soft iron and iW ii • 

 action of magnets and electric currents are peculiarly int. ix -: 

 ^ng- An approximate representation of the resultant line- ^-i 

 the terrestrial magnetic action has been obtained by magneti- 

 zing eqnahly tempered steel discs of fi'om 2 ins. to 3 ins., and 

 even more, in diameter. The magnetic axis or axes of these 

 discs are j)rec?efermmec? by making them the continuations of 

 the axes of very powerful electro-magnets, terminated with 

 cones of soft iron with slightly rounded apices. The arcs 

 01 the great circles, including the terrestrial magnetic poles, 

 h«^^^ng been calculated, the axes of the electro-magnets are 

 ned to that angle, while the steel disc is held close to 

 f poles. On passing the current the disc is magnetized 

 «uu we have an approximate representation of a section of 

 tne earth's magnetic effect These results when viewed as 

 Photographic prints, or, as exhibited by the lantern, are so 

 t^eautilul and instructive as to appear to me to warrant this 

 HrJ^**^*P^c prints from a seriea of eight of these plates I have presented to 

 BJ^aM College; American Academy of Sciences; r^--=~'^ «-=-"^'^'' '^^'^' 

 sitv p ^ollege; Stevens Institute of Technology, 

 Bali o' .-^erican Philosophical Society; Franklm In 

 ^.Smithsonian Institution; Chicago /"^ •• ' 



