1 10 Notices of the Proceedings of the S. A. Institution. 



(luce the sectiou or aperture to one square foot, the velocity 

 of efflux must be 40 miles ; and if it were four square feet, the 

 velocity would be 20 miles. In this last case, the pump must- 7 

 discharge at each stroke, as much as would fill a channel of 

 4 square feet, to the height of ten times the steam piston's 

 stroke. Even in this case the machinery will occupy much 

 room ; nor does the principle seem applicable to any case but 

 that formerly alluded to, when it may be required to produce 

 a suiall velocity by means of machinery defended against that. 



4. The fourth variety of propellers, is that in which the move- 

 ment is rectilineal, but the impact is oblique. Several pro- 

 posals of machinery of this kind have been offered. They 

 promise little advantage. The propellers may work on a plane 

 perpendicular to the vessel's course, either vertically or hori- 

 zontally, aria be completely under water ; and the return 

 stroke produces the same effect as the other directed out- 

 wards ; but there is here the disadvantage of oblique impact 

 already mentioned, that the velocity of the striking surface 

 must be double that of the stream which it generates. The 

 machinery would be cumbrous, and easily disarranged. 



It will be ovious from this analysis, that the ordinary re- 

 volving paddle-wheel is superior to other contrivances for 

 comrnoA navigation by vessels of burden. 



Where so great an extent of cooling surface could be so 

 readily piocurcd, the proposal to employ alcohol, or brandy, 

 in place of watr-r, to produce an expensive vapour, is worthy 

 of attention. What we know of the specific heat of these 

 substances encourages the experiment. The waste of material 

 might, from the circumstance above-mentioned, be almost en- 

 tirely prevented. 



The easiest and most effective method of producing a slow 

 movement, in some cases, may be found in the employment of 

 an explosive mixture, such as crushed gunpowder. Its power 

 might be applied directly to the water in a tube passing through 

 the vessel, or to water contained in a strong cylinder rising 

 from such a tube; presenting a machine of very simple struc- 

 ture. This would be the moving power of the rocket more ad- 

 vantageously employed. The effect may be understood by 

 conceiving the coll of a long gun fired underwater. A small 

 proportion of the powder spent in firing the broadside of a 

 ship, might in this way produce a decisive effect upon her 

 position. 



October 10. — A collection of specimens sent by Dr. Smith, 

 was presented, consisting of 828 articles, of which 119 were' 

 ordered to be added to the Museum. 



