BY COMPRESSION, 309 



tltat amount. To have a just estimate, then, of the quantity of 

 water displaced by the solid body, the apparent loss of weight 

 must be increased by adding the absorption to it. 



Two distinct methods of talking specific gravity thus present 

 themselves, which it is of importance to keep separate, as each 

 of them is applicable lo a particular class of subjects. 



One of these methods, consists in comparing a cubic inch of 

 9, substance in its dry state, allowing its pores to have their share 

 in constituting its bulk, with a cubic inch of water. 



The other depends upon comparing a cubic inch of the SO'^ 

 Jid matter of which the substance is composed, independentl3'^ 

 of vacuities, and supposing the whole reduced to perfect solidity, 

 with a cubic inch of water. 



Thus, were an architect to compute the efficacy of a giveii 

 bulk of earth, intended to load an abutment, which earth was 

 dry, and should always remain so, he would undoubtedly follow 

 the first of these modes ; Where&s, were a farmer to compare 

 the specific gravity of the same earth with that of any other 

 soil, in an agricultural point of view, he would use the second 

 jnode, which is involved in that laid down by Mr. Davy. 



As our object is to compare the specific density of these re- 

 sults, and to ascertain to what amount the particles have ap» 

 proached each otner, it seems quite evident that the first mode 

 is suited to our purpose. This will appear most distinctly, by 

 inspection of the following table, which has been constructed 

 ^0 as to include both. 



TABLE 



