808 
]ME. W. HOPKINS’S EXPEEIMEXTAL EESEAECHES 
Argillaceous substances. 
Dry clay ‘27 
Very dry ■23 
Moist ‘37 
Siliceous rocks. 
New Red Sandstone (dry) 
New Red Sandstone (saturated with water) 
Sandstone for building (freestone) 
Sandstone for building 
Millstone-grit (partially decomposed) 
Millstone-grit 
Millstone-grit from the coal-shaft at Duckenfield, at depth of 120 
feet 
Millstone-grit from deeper beds 
Millstone-grit from the depth of 1300 feet, and very hard . 
Millstone-grit from Chapel-le-Frith, used for pa’ving-stone at Man- 
chester, very hard 
Millstone-grit from Chapel-le-Frith, used for pa\ing-stone at Man- 
chester, very hard 
•25 
•60 
•33 
•43 
•376 
•58 
}-ol 
•65 
•726 
■75 
•76 
Old Sedimentary rocks. 
Blue, hard, close-grained rock from Penmaenmaur, used for pacing- '| 
stone . . ./ 
A similar specimen ... -6 
Blue, hard, compact slate from Charnwood Forest -61 
Igneous rocks. 
Granite •53 
Scotch granite, used for paving at Manchester -55 
A hard compact rock from North Wales (called Welsh granite) . . •dO 
Scotch granite, rather large-grained -75 
Basalt from near Loch Katrine -53 
Syenite from Charnwood Forest *85 
A very hard, close-grained rock from Charnwood Forest . . . . -99 
Igneous rock from Loch Katrine 1-0 
Basalt from the same locality -59 
Mountsorrel granite -8 
A great number of experiments were also made to determine the influence of pressure 
discontinuity, temperature and moisture on the conductive powers of -carious substances 
I proceed to state the general results of them. 
