u04i Thichiess, Cement and Materials of JValls^ 



Otherwise * as has been observed in the instance (though 

 it is not singular) of the stone work of the Schuylkill 

 bridge; which will long afford, under our own view, 

 facts, proofs and examplesj for most of the operations, 

 and component parts of strong and massive masonry. 

 It has been the over richness of the mortar, that has 

 suggested this mistaken opinion.* The cement will 

 sohdify, if properly composed, wherever there is a?r.* 

 and it is well known, that this subtile fiuid pervades all 

 matter* If it were not otherwise proved, as it often has 

 been, both philosophically and experimentally ; the in- 

 stances of toads and Jfogs, found in perfect animation, 

 in the midst of solid blocks of marble, and granite, 

 would be sufficient, ^ir must be inhaled for respira- 

 tion, and mustexist (as it is essential to life) in the stone; 

 and communicate with, and circulate through, the com- 

 mon atmosphere, so as to bring fresh supplies, and car- 

 ry off the mephitic; or these animals, thus isolated, 

 would soon perish , if they could begin their existence ; 

 though they are said to require a less portion of air^ 

 than others, t There is no recess so retired, as to es- 



* A decided proof of this, is mentioned in one of the re- 

 ports of the committee, who superintended the building of 

 this bridge ; in the account of the masoniy intended for a 

 pier; but abandoned, as to its use, in that capacity. See 

 Statistical Accoujit, Page 41. 



f Like all reptiles and amphibious animals, they can live 

 with less air, than is usually required by others ; yet it does 

 not follow that they can exist without it. Some have doubt- 

 ed their being furnished with the organs of resp'ration. But 

 I have, while attending experiments with the air pump^ seen 

 them die in an exhausted receiver. 



