308 ACTION OF HEAT MODIFIED 



influence in circumstances and in combinations hitherto untried, 

 that many of its branches must still remain in an unfinished 

 state, and may long be exposed to partial and plausible objec- 

 tions, after we are satisfied with regard to its fundamental doc- 

 trines. In the mean time I trust, that the object of our pur- 

 suit has been accomplished, in a satisfactory manner, by 

 the fusion of limestone under pressure. This single result af? 

 fords, I conceive, a strong presumption in favour of the solu- 

 tion which Dr, Hutton has advanced of all the geological phe- 

 nomena ; for, the truth of the most doubtful principle which 

 ho has assunaed, has thus been established by direct experiment. 



APPENDIX, 



No. I. 



Specific Gravity of some of the foregoing Results, 



Concerning the As many of the artificial limestones and marbles produced ir* 

 ties of bodies- ^-^i^^se experiments, M'ere possessed of great hardness and com- 

 paiticularly pactncss, and as they had visibly undergone a great diminution 

 ous : the a<^Ve- ^^ Ijulk, and felt heavy in the hand, it seemed to me an object of 

 gate i>ein2: less some consequence to ascertain their specific gravity, compared 

 ally, than the ^^^^ ^^^'^ other, and with the original substances from which 

 parts separate- they were formed. As the original was commonly a mass of 

 iy taken. i n ■ . i i • i ■ " t ■, • i • 



chalk HI the lump, which, ou being plunged into water, begins 



to absorb it rapidly, and continues to do so during a long time, 

 so as to vary the weight at every instant, it was impossible, till 

 the absorption was complete, to obtain any certain result ; and 

 to allow for the weight thus gained, required the application of 

 a method different from that usually employed in estimating spe= 

 cific gravity. 



In the common method, the substance is first weighed in air, 

 and then in water ; the difference indicating the weight of wa- 

 ter displaced, and being considered as that of a quantity of wa- 

 ter equal in bulk to the solid body. But as chalk, when satu- 

 rated with water, is heavier, by about one-fourth, than wlien 

 dry, it is evident, that its ipparent weight, in water, must be in= 

 creased, and the apparent loss of weight diminisiicd exactly to 



that 



