571 FOURTH REPORT — 1834. 



of the same vein. Galena, and copper, and iron pyrites are the 

 only substances usually met with in the Cornish mines which are 

 capable of conducting voltaic electricity; and as iron pyrites is 

 much more generally found in insulated masses than the other 

 two, the test here suggested may be employed with a consi- 

 derable degree of confidence on many occasions. 



It was in Huel Jewel, and more than four years ago, that the 

 author first obtained electro-magnetic results. The workings 

 have been so much extended since, that the last experiments 

 were made 60 fathoms deeper, and at least 80 fathoms further 

 towards the east, than the first ; and it is satisfactory to find 

 that the direction of the electricity remains unchanged, viz. 

 positive from the east. The temperature at the bottom level 

 of the mine, 38 fathoms under the surface, was then 59°, and it is 

 now, at the depth of 108 fathoms, 70°. The author has observed 

 that when the sulphuret of copper or of lead is heated, or even 

 slightly warmed, it becomes positively electrical, and yet the 

 deepest parts of the veins of those ores, although warmer than 

 nearer the surface, appear generally to be negative. 



Notice respecting a reynarkable Specimen of Amber. By Sir 

 David Brewster, F.R.S. 



This specimen of amber was brought from India by Mr. 

 Swinton, and was found in the kingdom of Ava. Its size is 

 nearly equal to that of a child's head, and its general aspect and 

 physical properties, seem to differ considerably from the ordi- 

 nary specimens of amber. The remarkable fact, however, which 

 distinguishes it from all specimens of amber which the author 

 has seen or read of, is that it is intersected in various directions 

 by thin veins of a crystallized mineral substance. These veins, 

 which cross one another, are sometimes as thin as a sheet of 

 paper, and in other places about the twentieth of an inch thick. 

 In order to determine the nature of the mineral, he extracted 

 a portion of the thickest vein; and having obtained, by cleavage, 

 a small rhomb, succeeded in measuring the inclination of its 

 planes, and found it to be a carbonate of lime. The specimen, 

 however, did not enable him to ascertain whether the angle was 

 that of the pure carbonate of lime, or that of carbonate of 

 lime and magnesia. 



At the next meeting of the Association, the author hoped to 

 be able to bring forward a detailed account of this curious 

 specimen, and to exhibit it to the Section ; but he considered 

 the single fact which he had now mentioned as calculated to 

 throw so much light on the origin of amber, that he trusted it 



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