432 Mr.Pndeauxonthe [Dec; 



stance. I applied heat to a specimen of the wood, but it only 

 became hot giving off the acid, &c. ; it effervesces with muriatic 

 acid very strongly. If you think these curious facts worthy of 

 a place in the Annals of F/iilosophy, they may probably induce 

 some of your readers to offer a theory to elucidate these very 

 natural questions ; viz. Why the shells are unaltered in all the 

 cliaracteristic properties of wood? And why the fragments of the 

 wood and the nuts (which were all found together) have under- 

 gone a perfect change? Whether we may consider the shells 

 preserved (chemically) by essential oil of the nuts, bitumen, or 

 the adventitious circumstance of being impregnated with sulphur? 

 I remain, Gentlemen, your very obedient servant, 



J. L. Levison^t 



P. S. I shall be most happy to give you or any of your corre- 

 spondents ocular proof of the facts stated, by calling on me. 



*^* Specimens of fossil nuts, precisely similar to those de- 

 scribed by Mr. Levison, may be seen in the British Museum : 

 they are from Carrickfergus Bay. — Edit, 



Article VI. 



On the Advantages of High Pressure Steam. 

 By Mr. John Prideaux. 



(To the Editors of the Annals of Philosophy,) 



GENTLEMEN, Plymouth, Oct. 4, 1825. 



If the following obvious remarks have been any where anti- 

 cipated, this letter may be destroyed. But having seen an 

 attempted demonstration in your fourth volume, and heard it 

 lately repeated by distinguished practical engineers, that 7io 

 direct advantage results from the use of high pressure in steam 

 engines J because the force of steam is as its density, and its caloric 

 a constant quantity at all densities, thus making the force just 

 proportional to the fuel employed ; it seemed to me worth while 

 to occupy one or two of your pages with what I apprehend to be 

 a more correct view of the subject. 



It is established by sufficient experiments, 



1 . That the caloric of steam, in contact with water, is a con- 

 stant quantity at all temperatures. 



2. 1 hat every elastic fluid, at a given density, has its expansive 

 force in proportion to its temperature, increasing ^^ for each 

 ascending degree of Fahrenheit. 



3. That every elastic fluid, at a given temperature, has its 

 expansive force directly as its density. 



