318 Proceedings of Learned Societies. 



it was quite a mistake to Lang curtains in front of pictures with a 

 view to their protection. 



Mr. Pengelly made some very interesting observations on the 

 insulation of St. Michael's Mount, Cornwall, which is now an island 

 at high tide, arid a peninsula at low water. The early British name 

 of the mount signifies the " hoar rock in the wood," a description 

 that is no longer applicable ; bub the change must have taken 

 place before the time of Diodorus Siculus, who wrote 9 B.C., as he 

 described the mount as it exists at present. Mr. Pengelly rejected 

 tbe theory that the rock had been insulated by the encroachment 

 of the sea, and maintained that its present condition was due to a 

 general subsidence of the land. In the observations which followed 

 the reading of the paper, Sir Charles Lyell supported the views of 

 Mr. Pengelly, and said that there had been considerable changes of 

 level since the ancient workers in tin had carried on their labours. 

 There had certainly been a submergence and deposit, and then a 

 re-elevation of many parts of the country since that time, and that 

 the proof of this was highly interesting as showing that great 

 changes had been effected in the condition of the globe during the 

 human period. 



Among the improvements in practical science brought forward 

 at the Association, may be described the utilization of blast furnace 

 slag as practised in Prance and Belgium. The plan there pursued 

 is to run the slag direct from the furnaces into a pit eight or nine 

 feet in diameter, and three feet in depth ; in these it is allowed to 

 cool slowly, which requires eight or nine days, when the solid 

 mass is removed and cut into slabs of the required size for paving 

 stones, for which purpose it is used in many of the towns of Prance 

 and Belgium, and some of the streets of Paris, and is found to be 

 superior to the sandstones and grits usually employed in those 

 countries where there is a great deficiency of good paving stones. 

 Whether the plan would answer conveniently in this country remains 

 to be proved, as we possess a greater supply of good stones, and 

 the space required for the pits would be a serious drawback to the 

 introduction of the process, and there is much difference in the 

 slags from different furnaces. 



The unstable equilibrium of the elements of gun-cotton was 

 strikingly shown by some experiments detailed by Mr. Scott, who 

 found that either of the metals, potassium or sodium, produced 

 an immediate explosion of this substance even when in a perfectly 

 anhydrous condition, none of the other metals appeared to 

 possess the same power as those of the alkalies, and even an amalgam 

 of potassium or sodium is inert. The singular result of the 

 contact of potassium or sodium with the cotton appears due to 

 direct chemical action, and not to the presence of water or moisture 

 inflaming the metal. It may be stated that gun-cotton is now being 

 manufactured for use in ordinary breech loaders by Messrs. Prentice, 

 and is found to be perfectly safe and to possess a higher penetrating 

 power, and to cause much less recoil than common gunpowder. 



