322 Proceedings of the Glasgow Pkilosophi<fal Society. 



Into the subject of damp walls in general, it is not my intention 

 in the meantime to enter, as that may be better taken up separately. 

 I may mention, however, in connection with this subject, that bricks are 

 generally as absorbent as stone. The average absorption in those I have 

 tried is about 10 per cent, of their weight. 



I have now only to refer to one or two other characteristics of our 

 building stones, arising in a great measui-e, I think, from the clay they 

 contain. First, the rapidity with which they become black by exposure. 

 The cause is no doubt the smoke, but the clay in the stone makes this 

 colouring much more rapid from the great attraction which alumina has 

 for colouring and organic matters. A house built of such stone as 

 Craigleith, and one with a sandstone containing 20 per cent, of clay in 

 the same locality, the one would become much sooner coloured than the 

 other. 



Another tendency which sandstone has is to become covered with a 

 vegetable growth, and the question has often been put where the seeds 

 of such vegetable matter may have come from. Now, there could hardly 

 be a better condition for the growth of vegetable mould than a sandstone 

 having diffused through it mechanically from 15 to 20 per cent, of clay, 

 with a little lime and magnesia, and capable of absorbing within a few 

 hours several gallons of the moistui'e of a soil, and no doubt the sporules or 

 seeds of such vegetables either in soils or floating about the atmosphere, 

 are either drawn up by and with the water from the soil, or they attach 

 themselves to the surface of the stone, and find there ample means for 

 their development. 



Such, then, are a few experiments and observations upon a subject, I 

 think, deserving a more thorough investigation. I have been induced to 

 bring it before the Society in this unfinished state by a strong desire 

 that those who may be interested in this matter, and who have oppor- 

 tunities of furnishing specimens old and new, so that unquestionable data 

 may be obtained, will be kind enough to let me have them, with any 

 particulars they may consider necessary, with a view to bringing the 

 results before the Society at a future time, should health be granted. 



Mr. Ure exhibited an improved form of his Model illustrating the 

 Principle of Ventilation. 



Minute of Council. 

 Andersonian University Library, November 3, 1852. 



Present, Mr. Crum, Dr. Allen Thomson, Dr. A. K. Young, Mr. Liddell, 

 Dr. R. D. Thomson, Mr. Gourlie, Mr. Bryce, Mr. Harvey, Mr. Cockey, 

 Mr. Murray, Dr. Mitchell. 



Dr. Arthur Mitchell, after some explanatory remarks, produced the 



