On Earthquakes and Volcanos. 21 



lirated and compressed, is deduced by analogy, from what 

 happens at the surface, as is explained in the article itself. 



No. 8. The best answer to this last, and perhaps to all the 

 other objections, is to copy here an extract of the Philoso- 

 phical Transactions, 1826. On Compression of Atmos- 

 pheric Air, by Perkins. " In the course of my experiments 

 on the compression of atmospheric air, I observed a curious 

 fact, which induced me to extend the experiment ; viz : that 

 of the air beginning to disappear at a pressure of five hun- 

 dred atmospheres, evidently by a partial liquefaction, which 

 is indicated by the quicksilver not settling down to a level 

 with its surface. At an increased pressure of six hundred 

 atmospheres, the quicksilver was suspended about one-eighth, 

 of the volume up the tube or gasometer. At eight hundred 

 atmospheres it remained about one-third up the tube ; at one 

 thousand atmospheres, two-thirds up the tube, and small 

 globules of liquid began to form about the top of it ; at 

 twelve hundred atmospheres the quicksilver remained three- 

 quarters up the tube, and a beautiful transparent liquid was 

 seen on the surface of the quicksilver, in quantity about -T^-^-go 

 part of the column of air." 



From these experiments, it follows as a fact, that under 

 the pressure of eight hundred atmospheres, two-thirds of the 

 air is still under an aerial form, although its density is then 

 equal to that of water ; and even at twelve hundred, when it 

 is much denser, one-third of it is not liquefied. This is suffi- 

 cient for us to maintain that under the pressure of the sea a 

 layer of air may produce the eflTects we have endeavored to 

 describe. 



N. B. We regret that the beautiful experiments of Mr. 

 Perkins on the compressibility of water have not been per- 

 formed upon water at forty degrees of temperature, its great- 

 est natural condensation, instead of fifty degrees, and upon 

 water entirely deprived of air ; this would be a still greater 

 proof that water itself is condensed, and not the air it con- 

 tains, or not that the caloric, which dilates it, is repelled by 

 compression. By similar reasons, the compression of air 

 should have been performed on air perfectly dry, that it might 

 not be objected that some water has been liquefied ; and the 

 experiment performed also on oxygen and azote separately, 

 to show, whether these gases hquefy each at the same pres- 

 sure when they are not combined as in the atmospheric 

 air. 



