278 Mr Harker, Magnetic Disturbances in the Isle of Ski/e. 



the mass of the rock, without parallelism of their axes and, 

 according to most observers, without any ascertainable law of 

 arrangement. The property is described as residing only in the 

 more superficial parts of a rock-mass, but the inferences drawn 

 from this distribution are not always concordant. For example, 

 Zaddach 1 connected the magnetic polarity with chemical altera- 

 tion of the rock by atmospheric agency ; a hypothesis not in itself 

 very plausible, since one chief result of such weathering would be 

 the conversion of the magnetic oxide to the peroxide or hydrated 

 peroxide. The magnetic basalts and gabbros in Skye are often 

 perfectly fresh, and the property is confined to rocks which are 

 not only exposed to the atmosphere but exposed in prominent 

 situations. 



EXPLANATION OF PLATES. 



Plate xi. Ground-plan of the summit of Glamaig. The arrows show 

 the positions assumed by the needle at differt nt spots. The numbers 

 are not declinations, but deviations from the normal magnetic - meridian 

 for the time and place (N. 21° W.), reckoned positive towards the left 

 and negative towards the right. The asterisks mark places where 

 violent local disturbances occur in consequence of strong polarity o!' the 

 rocks. 



Plate xii. Behaviour of the compass needle on the prominent ridge 

 of Meall an Ehuarain. The observations are marked on a ground-plan, 

 and longitudinal and transverse profiles of the ridge are added to show 

 the form of the ground. The numbers give, in degrees, the deflections 

 from the normal magnetic meridian (N. 21° W.), reckoned positive 

 towards the left and negative towards the right. Many observations 

 have been omitted to avoid confusing the diagram : they are in all cases 

 in accoi'd with the observations actually shown. The asterisks mark 

 the chief places of violent local disturbance due to strong polarity of the 

 rocks. 



On Differential Equations with two Independent Variables. By 

 A. C. Dixon. 



[Head 5 February 1900.] 

 v. Transactions, Vol. xix. Part I. 



] Verh. natnrh. Vereins, Bonn, vol. vm. , pp. 195 — 306, plates n. — iv. ; 1851. 

 Besides a minute description of certain magnetic crags of basalt, this paper contains 

 a review of the earlier literature of the subject. For a more complete bibliography 

 see Meli, Boll. Soc. Geol. Ital, vol. ix., pp. 645—670; 1881. 



