174 Prof. J. Noggerath on the Magnetic Polarity 



immensely large, will in all probability be greater than «, 

 <p will be greater as \ is greater. Therefore m will be less as 

 X is greater. Hence the rays for which A is greatest, that is 

 the least refrangible rays, will be propagated with the greatest 

 velocity. Also the velocity of propagation is independent of 

 the intensity of the rays. These results are conformable with 

 experience. 



As n is probably exceedingly small compared with — — * 



it is possible that \ may have a value much larger than it has 

 for luminous waves, and cot <p not change sign in consequence, 

 but become very small. Then cos $ would = 0, and m = 1 

 nearly. Thus there may be aethereal undulations much 

 broader than those which cause light, that do not undergo 

 sensible change in their velocity of propagation, as they enter 

 mediums. 



XXVIII. On the Magnetic Polarity of two Mocks of Basalt 

 near Nilrburg in the JEifel, with some Observations on the 

 extension of Basalt in that district ; drawn up from the Ob- 

 servations <9/"Bergmeister Schulze of ' Diiren. By Professor 

 J. Noggerath.* 



CINCE the discovery, by Alexander Von Humboldt, of the 

 ^ magneto-polar property of a rock of serpentine on the 

 Haidberg or Heideberg, near Celle, in the country of Baireuth, 

 many other rocks have been found possessed of the same pro- 

 perty, viz. : serpentine, and rocks of other kinds, such as horn- 

 blende-slate, porphyry, trachyte, basalts, &c.f 



It seems, however, to be found only in mountains contain- 

 ing magnetic iron-stone, although the quantity of this admix- 

 ture in itself does not limit the intensity of this property ; as 

 indeed it shows itself with different purely magnetic iron- 

 stones in the greatest variety of degrees of strength, and there 

 are some of these which show no magneto-polar action. 



Nor does there appear, from all the observations made on 

 magneto-polar rocks and fragments, that there is any regula- 



* From Schweigger's Journal. 



f For the discovery of Humboldt and those connected with it, see in 

 particular the Intelligenz Blatt ofJenaer Algemeine Literaturzeitung, 1796, 

 No. 169, p. 1447; ibid. 1797, No. 38, p. 323; No. 68, p. 564; and No. 87, 

 p. 722. Neues Bergmann's Journal, i. pp. 257 & 542. Gren's Neues 

 Journ. d. Chem. u. Phys. iv. Heft i. p. 136. V. Moll's Jahrbuch d. Berg u. 

 Hidtcn Kunde, iii. p. 301. V. Moll's Neues Jahrbuch d. B. u. H. ii. p. 403. 

 Gilbert's Annalen, neue Folge xiv. Heft i. p. 89. Goldfusz and Bischof 's 

 Phisik. statist. Bcschreibung d. Fichtelgcbirgcs, i, p. 139. and ibid, altere 

 Reihe xviii. p. 297. 



rity 



