404 Proceedings of the Royal Irish Academy. 



Fortunately this difficulty is considerably lessened by the fact that 

 only small quantities of minerals are required, and these can often be 

 obtained from a museum specimen without injuring the specimens in 

 any way. 



In many cases without a quantitative analysis it is quite impos- 

 sible to give the composition of a mineral with accuracy. In such 

 cases all one can do is to give the locality from which the specimen 

 was obtained as a clue to possible peculiarities in its composition ; 

 although in the exact sense one would not be likely to find many 

 specimens of exactly the same chemical composition even when taken 

 from the same locality. 



Small variations in chemical compositions do not appear to effect 

 the molting point seriously. Several specimens of the same minerals 

 from different localities show melting points that vary very little ; 

 only about 2 or 3 per cent, as will be seen by the tables at the end. 

 Thus a specimen of augite from Terra del Fuego and one from 

 Yesuvius differed in their melting points only by 12°. That from the 

 former melted at 1187°, and the latter melted at 1199° C. 



"WTien one finds that the hardness and specific gravity of two 

 specimens of augite vary very considerably with their composition, it 

 is not surprising to find that their melting points also vary some- 

 what. But whereas in extreme cases the specific gravity of augite 

 varies nearly 10 per cent., the melting point only varies, as far as 

 observations have been made, 1 per cent. The greatest variation 

 observed is that of Diallage, one specimen melting at 1264°, and 

 another at 1300°. In this case I may have chanced to hit on extreme 

 specimens, for the first specimen melted at 1300°, and the second I 

 tried melted at 1264°, but when the other three specimens I had 

 obtained were determined it was found that they only varied 14°. 

 Diallage is slightly viscous, so has no definite melting point. I have 

 to thank Dr. Sollas for his kindness in giving me out of the museum 

 several specimens I would otherwise have been unable to obtain : 

 and I have also to thank Dr. Joly for his kindness in lending me 

 instruments, for many specimens, and for the assistance he frequently 

 gave me. 



It would be interesting perhaps to give an account of the behaviour 

 of some of the specimens when on the ribbon. 



Actinolite. — Of the four specimens examined, three were of the light 

 green fibrous variety, and one a dark olive green crystal quite destitute 

 of fibrous structure, and yet the melting points differ by only 16°, that 

 of the granular specimen being the lowest ; this might be accounted 



