246 Col. Beaufoy on the Spiral Oar. [Oct. 



afterwards I repeated the experiment with a view to find whether 

 any carbonic oxide was mixed with the acid ; the lamp was 

 burned under a bell glass of 120 cubic inches till the redness of 

 the wire ceased to be visible in the dark, when a phial of the 

 air was extracted for examination ; as soon as the bell glass was 

 removed, the wire resumed its original glow again, which 

 showed that the combustion had not ceased. On examining the 

 air over mercury in the usual manner, I found it contained 14|- 

 per cent, of oxygen and about four per cent, carbonic acid ; but 

 I could discover no more carbonic acid by firing the residue with 

 the addition of hydrogen and a little oxygen. 



Thus it appeared that my conjecture respecting the produc- 

 tion of carbonic oxide was not supported by experiment ; this 

 kind of combustion proved to be rather more than less vigorous 

 than the ordinary one, as the oxygen was reduced rather more 

 than it would have been by the common combustion carried 

 to extinction. 



In order to examine this last point more fully, I caused the 

 lamp to burn with flame under the same bell glass filled with 

 atmospheric air, till it was extinguished spontaneously. The 

 residuary gas was found to consist of 16-i- per cent, oxygen, and 

 three carbonic acid. Again, the lamp without flame was burned 

 under the same glass in like circumstances, and kept for 40 

 minutes, when it was quite extinct ; the residuary air being 

 examined was found to contain only eight per cent, oxygen, and 

 nearly the same quantity of carbonic acid. 



I have frequently found on former occasions that the combus- 

 tion of oil, wax, tallow, &c. all reduce the oxygen nearly in the 

 same degree before the combustion is extinguished, namely, 

 four, five, or six per cent, it being 21 per cent, at the commence- 

 ment. It appears to me, therefore, a very singular and remark- 

 able fact, that this species of combustion should be enabled to 

 reduce the oxygen so much, or to support itself in circumstances 

 in which the ordinary one entirely fails. 



I remain, yours truly, 



John Dalton, 



Article III. 



Observations on the Spiral as a Motive Power to impel Ships 

 through the Water, with Remarks when applied to measure the 

 Velocity of Water and Wind. By Col. Beaufoy, F.R.S. 



(To the Editors of the Annals of Philosophy.) 



GENTLEMEN, Bushey Heath, July 22, 1818. 



In the Annals of Philosophy for last June, an ingenious plan 

 is given for impelling vessels through the water with, a spiral oar, 



