Roycd Institution of Great Britain. 189 



112° is equal only to 2 J inches of mercury ; the elastic force, there- 

 fore, of the vapour produced at 6 J 2° would, when cooled to 512°, 

 be also equal only to 2 J inches of mercury. There is, it must be 

 confessed, a difficulty in condensin*^ by mere contact with a me- 

 tallic surface, as compared with condensation by an injection : but 

 this difficulty would, in the proposed case, be much less than in 

 the various schemes which have been projected to use alcohol, 

 ether, and liquid carbonic acid, because in the former it is pro- 

 posed to cool a less easily vaporized substance by one more easily 

 vaporized ; whereas, in the latter cases, water, which has been the 

 intended cooling material, is less easily vaporized than the sub- 

 stances it is required to cool ; a circumstance obviously unfavour- 

 able to the production of the effect. But for this difficulty, it is 

 probable that the heat employed to vaporize water might, by the 

 condensation of the steam, be transferred to alcohol, and from this 

 again to the ether ; but the question then arises, how is the heat to 

 be abstracted from the ether ; we have no other means than the con- 

 tact of a vessel containing cold water, a means v/hich is found in- 

 sufficient for cooling common steam, and which would, therefore, 

 be doubly inefficient in cooling the vapour of ether. These consi- 

 derations will suggest other difficulties in the construction of en- 

 gines to use alcohol and ether, beyond the absolute defect of 

 economy, which has been before explained. 



February 26th. 



This evening Mr. Watson developed his plan for preventing ships 

 from foundering at sea. This plan, as is well known, consists in 

 introducing air-tight copper tubes into various parts of the ship, so 

 as to be out of the way, and yet, by their buoyancy when immersed 

 in water, prevent the ship from sinking when full of the fluid. Mr. 

 Watson illustrated his plan by experiments on the buoyancy of dif- 

 ferent kinds of wood, and also by models of an 80-gun ship, fur- 

 nished with air-tubes. The plan is so fully before the public in 

 various forms, that we do not think it necessary to enter into fur- 

 ther details here. 



In the library Captain Grover exhibited a Wollaston's double 

 microscope, made after the model left by Dr. WoUaston to Captain 

 Kater, and the first that had been constructed. Its performance 

 was admirable. 



