}818.] Crystalline Form and Chemical Composition. 271 



form, until the proportions are ascertained in which the earths 

 combine ; and we are thus directed with certainty to the mode 

 of double classification. 



An extract of the report of Messrs. Haiiy, Vauquelin, and 

 Brochant, on the memoir, is appended to it in the pamphlet. 

 This report approves the deductions of the author in favour of 

 the crystallographical character as a basis of arrangement. It 

 also replies to an objection, which the facts contained in the 

 memoir may be supposed to raise, against the adoption of this 

 basis, by saying that all which crystallography attempts to 

 decide is, that sulphate of iron is present whenever the crystal 

 of sulphate of iron is produced, and that felspar is present when- 

 ever the crystal of felspar is formed. 



Article IV. 



A Plan for a Fire Ship. 



(To Dr. Thomson.) 



M;Y DEAR SIR, Bushty Heath, Feb. I, 1813. 



The following plan, which I proposed in the year 1804, for the 

 destruction of the enemy's flotilla, being now to a certain degree 

 known, I send it, with your permission, for publication in the 

 Annals of Philosophy. It is but fair that we should derive advan- 

 tage from the invention of our countrymen, and not be doubly 

 annoyed, as in the case of the torpedoes used by the Americans 

 against our men of war, by having our own weapons turned 

 against ourselves, and arming our foes to our own destruction. 

 I have no doubt but that a fire ship steered as described in the 

 following page, might be sent down and fall on board a large 

 vessel laying-to to leeward before she could brace about the sails 

 and gain sufficient way to avoid it. 



I remain, my dear Sir, yours very sincerely, 



Mark Beaufoy. 



It is proposed that a vessel, loaded as a fire ship with combus- 

 tible materials, should cany at its mast's head a large flag 

 (after the manner of a vane), attached to a spindle passed abaft 

 the mast, through one or more iron rings, and turning in a socket 

 on the deck : near the lower part of the spindle must be affixed 

 the segment of a large cog wheel running into another corre- 

 spondent with it at the end of the tiller, which is to be con- 

 structed of a due length for the purpose. The vessel then under 

 sail being put before the wind, with the helm amidship, will 

 continue to proceed in that direction ; because at the instant of 



