Miscellanies. 351 



duced a building best suited to the hearing of a speaker in many di- 

 rections. 



Resistance of fluids to bodies moving in them. — Mr. Russell sta- 

 ted, that the law of resistance most relied on since the days of New- 

 ton, was that the resistance increased as the square of the velocity, 

 and that this law did not cease until the resistance became very great. 

 But there is a wide difference between a body totally immersed and 

 one. partially floating. Mr. Russell had been enabled, by the liber- 

 ality of the canal commissioners, to make experiments upon a very 

 great scale ; the result is, that a canal boat is more and more retard- 

 ed, up to a certain velocity, when the resistance becomes a maxi- 

 mum ; and that, beyond this, the velocity being increased, the re- 

 sistance actually diminished, and consequently the force of traction 

 required to keep up that velocity, was less than the force of traction 

 required to keep up a less ; by which it happened that there was a 

 velocity, below which it would be less profitable for a ship or a boat 

 to be propelled, than any velocity above it, a circumstance of no 

 small importance to canal companies. 



Consumption of coal in steam engines. — Mr. Taylor stated, that 

 the. work done, in the best engines now employed in Cornwall, by 

 the consumption of one bushel of coals, required, ten or twelve years 

 ago, the consumption of two bushels ; that during the period of Bol- 

 ton and Watt's patent, four bushels were consumed to do the same 

 work ; and that, in the earlier stages of the employment of steam 

 power, the quantity of coal used was sixteen bushels. The steam 

 engines now at work, in the mines of Cornwall, are equal in power 

 to at least forty four thousand horses. 



Trap Dyl£es. — In the west of Ireland are many trap dykes, seven 

 of which, described by Archdeacon Verschoyle, run parallel through 

 the counties of Sligo and Mayo, for forty, fifty, and even sixty miles, 

 with a thickness often of forty feet. 



Prof. Sedgwick expressed his conviction, that the effect of trap 

 dykes on limestone, is to convert it into dolomite, by introducing 

 into it magnesia, in some unknown mode. 



Mr. J. Bryce stated, that when columnar trap is present in the 

 north of Ireland, chalk and other secondary rocks are generally ab- 

 sent, and that the Giant's Causeway does not, as is commonly sup- 

 posed, rest upon chalk rocks. 



Belemnitcs and Fishes, according to Prof. Phillips, are confined 

 to the chalk and oolites ; they have long since disappeared from the 



