414 Atmohjsis. 



with, the larger metamorphoses which we have been considering 

 in the present article. 



In conclusion, however, let the reader be advised, if not yet 

 familiar with the practical work of geology, to accept no 

 theory, and be bound by no respect for established authorities in 

 this matter. Geology is a subject for study, and not for dogmatic 

 statement. It is not desirable to raise another such storm as 

 that which disturbed the serenity of the scientific horizon when 

 the aqueous and igneous theories were first propounded. We 

 need not shut our eyes to truth because it seems opposed to 

 opinion, but we should observe closely and avoid coming to 

 conclusions too rapidly. Metamorphism is a great and difficult 

 subject. 



ATMOLTSIS. 



BY W. B. TEGETMEIEE. 



In the previous volumes of the Intellectual Observer* will be 

 found notices of the discovery of. the phenomena of Dialysis, by 

 Mr. Graham, the Master of the Mint ; of its application in the 

 explanation of natural occurrences, such as the formation of 

 minerals, and also of its practical utility when applied to the 

 arts of life and civilization. Mr. Graham has been continuing 

 these investigations with that profound originality of research 

 that has caused him to be regarded by scientific men as one of 

 the most illustrious investi orators , in the highest branches of 

 physical science. 



The phenomena attending the passage of liquids through 

 thin membranes constitute what is termed dialysis. Those 

 under consideration at present, depend on the passage of 

 gases through porous plates. 



Mr. Graham commenced this train of investigation many 

 years since, and, from time to time, some of his results have 

 been made known. The instrument originally employed in 

 these researches Avas termed a ditfusiometer, and consisted of 

 a plain, cylindrical glass tube, one inch in diameter, by ten 

 inches in length. Tins, by being closed at one end by a thin 

 plug of plaster of I'aris, was converted into a receiver capable 

 of being used over mercury. At the present time, compressed 

 graphite li;is been substituted for the plaster of Paris; this is 

 obtained by cutting slices with a fine steel spring-saw off the 

 compressed blocks used for the manufacture of pencils. These 

 slice's, by rubbing down on a dry sandstone, can be obtained 



* Intellectual Obseuvek, vol. i. pp. 15G and 381 ; vol. ii. p. 224. 



