1852.] OF THE ROYAL INSTITUTION. 138 
profess, she must inevitably and with rapidity lose those sources 
of power, which, in spite of the smallness of her home territory, 
have given to her so exalted a rank among nations. 
With these convictions you will not be surprised that I have 
chosen subjects connected with the Exhibition, although I have no 
merit or part whatever in their discovery. I have selected them for 
the following reasons. 
We have a great reliance on the practical sagacity or common 
sense of our population,—certainly superior to that of any part of 
Europe: but we have not strengthened it by communicating scien- 
tific knowledge to those who are entrusted with the exercise of this 
practical power; and, hence, this common sense, unaided by the 
rules of science, has gradually assumed a sway over our manufac- 
tures. In other words, conjectural judgments have usurped the 
place of systematic knowledge. Practice and science have been 
followed out separately, as having no immediate connection. This 
separation, and even practical antagonism, has been fatal to our pro- 
gress in industry; for manufacturers, as a body, have ceased to per- 
ceive that abstract science forms the roots of the tree of industry, 
and that to senarate them is to sever the tree from its roots. In 
order to restore vigour to our declining industry, it is essential that 
confidence in the powers of science should be imparted to practice, 
and that the latter should be taught that it is, even as a question of 
social policy, highly important to encourage discoveries in abstract 
* truths, however apparently remote from practice; because science 
only benefits industry by its overflowings, arising from the very 
fulness of its measure. 
Every abstract truth, in its due time, adds to human resources 
and enjoyments, and it is this text that I wish to inculcate from 
examples derived from the Exhibition. One of the last generaliza- 
tions of the great Berzelius, was that of allotropism, a name only 
eleven years old, and fully explained by him only six years since; 
and yet this generalization, apparently, at the time, only of abstract 
interest, entirely remote from practical application, produced as fruit 
the three most original, and, I think, the most important, practical 
discoveries of the Exhibition. 
Having thus introduced the subject of his Lecture, Dr. Playfair 
proceeded to offer certain examples of allotropism. It had long 
been known that bodies crystallized in two or more incompatible 
forms. Thus, carbonate of lime as arragonite crystallizes in prisms ; 
whereas as calcareous spar it crystallizes in rhombs. Sulphur also 
crystallizes in two incompatible forms ; so does the garnet. This is 
termed dimorphism. When two such forms exist they are found 
to be maintained in unequal stability ; it appears, in fact, as if one 
form was normal, and the other forced or strained. Thus a prism 
of arragonite is subject to change into rhombs of cale spar; and 
sulphur crystallized by heat in oblique rhombic prisms passes in a 
few days into a mass of rhombic octohedrons. Not only may the 
chemical and physical ‘characteristics of such dimorphous bodies 
