A. M. Mayer on fixing and exhibiting Magnetic Spectra. 2*]'^ 



strobiles, and of the stems and leaves of Ferns and l.vc.j , 

 and above all with the thick corky envelope of thr st.in^ 

 Sigillariae and similar trees, which as I have elsewluTi' >lu.\'. 

 from its condition in the prostrate and erect trunks (oiit;ii: 

 in the beds associated with coal, must have been liighlv ca. 

 naceous and extremely enduring and impermeable to \\u: 

 In short, if instead of "spore-cases," we read "epidermal : 

 sues in general, including spore-cases," all that Hnxlev i:- 

 affirmed will be strictly and literally true, and in accordance 

 with the chemical composition, microscopical charactei-s and 

 mode of occurrence of coal. It will also be in accordance with 

 the following statement, which I may be pardoned for quoting 

 from my paper on the Structures in Coal, published in 1859. 



" A single trunk of Sigillaria in an erect forest, presents an 

 epitome of a coal-seam. Its roots represent the Stigmaria under- 

 day ; its bark the compact coal ; its woody axis, the mineral 

 charcoal ; its fallen leaves (and fruits), with remains of herba- 

 ceous plants growing in its shade, mixed with a little earthy 

 matter, the layers of coarse coal. The condition of the dura- 

 ble outer bark of erect trees concurs ^vith the chemical theory 

 of coal, in showing the especial suitableness of this kind of tis- 

 sue for the production of the purer compact coals. It is also 

 probable that the comparative impenneability of the bark to 

 mineral infiltration, is of importance in this respect, enabling 

 tins material to remain unaffected by causes which have filled 

 rs consisting of herbaceous materials 

 y pyrites and other mineral substances." 



mose layers consisting of herbaceous materials and decayed 

 wood, with pyrites and o' " ' ' ' 



Art. XXXVIII. — On a method of fixing^ photographing and 

 by Alfred M. Mayer, 



^hibiting the Magnetic Spectra 



The figures produced in iron-filings, when these are set in 

 laomentary vibration on a surface placed over a magnet, have 

 received considerable attention from natural philosophers. The 

 geometrical discussion of these spectra made by Lambert, 

 ^oget and others, have developed their symmetrical properties, 

 and thereby have evolved the law of that action which ema- 

 nates from the magnet. De Haldat has used them as a means 

 ^J .exploring the distribution and intensity of the effect 

 ^ Juxtaposed magnets variously arranged- But, above all, 

 mnll^^^*^^^® structures in Coal. Joum. Geol. Soc, xr, 626. Conditions of Accu- 



f Sw." ^^*^5 i^- ^^"' 95. Acadian Geology. 197. 464. _ . , , • h« 



