HOUGHTON : ADDRESS. 
5 
even than to the general studies to which the society is ap- 
plying itself. The last volume of your transactions shows 
that this has not been hitherto neglected, and although I see 
that one of your members went so far out of the West 
Riding as to give us the German Ocean as the subject of a 
communication, yet, nevertheless, I am glad to see that the 
greater part of your later contributions and those to which 
we shall direct attention to-day are of a local character. 
Do not for a moment be led to consider that these observa- 
tions are of less importance because they are local. I am 
sure you will find that the leaders of science would say — 
Direct your attention to these local objects rather than 
attempt any generalisations, even though they may be of 
an original character. I do not say that you may not 
occasionally diversify your proceedings by generalisations; 
nevertheless, remember that the more provincial you are 
the better. 
OX A NEW METHOD OF STUDYING THE OPTICAL CHARACTERS 
OF MINERALS. 
BY H. C. SORBY, F.R.S., PRES.G.S., &c 
As is well known, the optical characters of minerals 
furnish us with a most valuable means for identifying the 
various species. The practical application of these phenomena 
has, however, been much restricted by the difficulty of 
obtaining crystals sufficiently large and transparent to be cut 
into appropriate sections, so that the properties of some of the 
commonest minerals were very imperfectly known. By the 
methods hitherto employed it was almost impossible to study 
the black or imperfectly transparent minerals constituting the 
chief part of rock masses, and in fact little could be learned 
unless the specimens were so large and perfect that the 
individual species could be identified by other means. What 
