206 Intelligence and Miscellaneous Articles. 



globulitic and crystallitic glass-basis of green colour, containing 

 spherules of quartz, spherulitic felspars, and an interesting series of 

 granules and granular aggregates of augite, which likewise frequently 

 assumed a spherulitic form. The rock was rendered microporphy- 

 ritic by the sparing development of crystals (or skeleton-crystals) of 

 plagioclase felspar, augite and quartz. The optical characters of 

 each of the minerals were given. Owing to the mode of develop- 

 ment and to the variety of its constituents, the rock possessed an 

 exceedingly complicated structure. The order of crystallization was 

 worked out, and it was pointed out that a second generation of each 

 of the important constituents had arisen. The second generation of 

 felspar was of a more acid type, and that of the quartz was devoid 

 of fluid vesicles, and had crystallized out after the rest of the rock 

 had solidified sufficiently to form cracks. Close physical and mi- 

 neralogical relations with the gabbro were indicated, and the author 

 had no doubt that the two were in actual connexion with one 

 another. The age was put down as probably Ordovician. A com- 

 parison of the rock with other basic rocks showed that it had 

 affinities both with the glassy forms connected with the more 

 volcanic members, and with the variolites of Durance found asso- 

 ciated with diabase. The relation with the latter rock was espe- 

 cially marked, but important points of difference rendered a separa- 

 tion of the two necessary, and for the new type of rock thus re- 

 cognized the name CarrocMte was suggested. This rock might be 

 looked upon as a Quartz-Gabhro-Vitrophyre. 



XXIV. Intelligence and Miscellaneous Articles. 



ON THE EFFECT OF TWIST IN MAGNETIZATION. 

 BY ME. H. NAGAOKA. 



To the Editors of tJie Philosophical Magazine and Journal. 



Gentlemen, 



IN a private letter to me, dated November 11, 1888, Mr. Na- 

 gaoka describes his further researches into the effect of tv^ist 

 in magnetization. His special object is to study the eiiect of dif- 

 ferent ranges of twist (i. e. the maximum twist to which the cycle 

 of twisting is can'ied). 



He finds that in iron the essential features of the curve of twist 

 and magnetism remain unchanged irrespective of the intensities of 

 either the magnetizing-field or the longitudinal stress. This con- 

 firms the results stated by Mr. Bottomley and myself in the latter 

 part of our note. When the range of twist is increased beyond 

 4-11° per centim. (a very large amount of twist), although the 

 general form of the curve remains similar, the hysteresis produced 

 by the cvcle of twisting and untwisting becomes reversed ; that is 

 to say, the untwisting part of the curve lies above the twisting 

 part, instead of being below, as it is when the range of twist is 

 moderate. In nickel the effect of range is more curious and in- 

 teresting ; but to describe even all that is in the letter will require 

 more space than I would dare ask in such a note as this. I may 



