248 Dr. Heddle and Mr. R. P. Greg on British Pectolites. 



magnet ; and therefore the niagnetiziug influence of a neigh- 

 bouring diamagnetic, which could scarcely, if at all, be observed 

 on a piece of soft iron, must be inappreciably small on another 

 diamagnetic. 



Cor. 9. All phaenomena of motion that have been observed as 

 produced in a diamagnetic body of any form or substance by the 

 action of fixed magnets or electro-magnets, are due to the result- 

 ant of forces urging all parts of it, and couples tending to turn 

 them ; the force aud couple acting on each small part being the 

 same as it would be if all the other parts were removed. 



Cor. 10. The deflecting power (observed aud measured by 

 Weber) with which a bar of non-crystalline bismuth, placed ver- 

 tically as core in a cylinder electro-magnet (a helix conveying an 

 electric current), urges a magnetized needle on a level with either 

 of its ends, is the reaction of a tendency of all parts of the bar 

 itself from places of stronger towards places of weaker force in 

 its actual field. 



The preceding investigation, leading to Props. VI. and VII., 

 is the same (only expressed in non-analytical language) as one 

 which was first published in the Cambridge and Dublin Mathe- 

 matical Journal, May 1846. The chief conclusions now drawn 

 from it, with particulars not repeated, were stated in a paper 

 entitled ' Remarks on the Forces experienced by inductively 

 magnetized Ferromagnetic or Diamagnetic Substances,' in the 

 Philosophical Magazine for October 1850. 



Glasgow College, 

 March 15, 1855. 



XXXVII. On British Pectolites. 

 By Dr. M. Forster Heddle, and R. P. Greg, Esq.* 



KOBELL'S mineral pectolite, found in the amygdaloid of 

 Monte Baldo in the Southern Tyrol, is introduced into 

 Dr. Thomson's ' Mineralogy ' with the original analysis (No. 16) 

 misquoted, the quantity of water being given as 8 - 89 instead of 

 3"89. This blunder explains the fact, that in another part of 

 his work, Thomson describes, under the name of JVollastonite, a 

 mineral found in greenstone near Kilsyth, which, however, is 

 evidently pectolite, the analysis (No. 2) also agreeing. 



Dr. Thomson states that the mineral he analysed was also 

 afterwards found by Lord Greenock in the neighbourhood of 

 Edinburgh, and Mr. Rose informs us that the precise locality 

 was the Costorphine Hill. Now Walker has given an analysis 

 (No. 3) of a mineral from the Costorphine Hill which is evi- 



* Communicated bv tbe Authors. 



