•bct. Ti.] DISSERTATION SECOND, 73 



ed, because a shorter column of air is to be sustained ; 

 the mercury in the barometer ought therefore to sink, 

 and it is found to do so accordingly. 



These are instances in which the action of certain 

 principles is rendered visible by the removal of all the 

 opposing forces. One may be given where it is the dis- 

 tinct and decisive nature of the fact which leads to the 

 result. 



Suppose it were inquired, whether the present land 

 had ever been covered by the sea. If we look at the 

 stratified form of so large a portion of the earth's surface, 

 we cannot but conclude it to be very probable that such 

 land was formed at the bottom of the sea. But the deci- 

 sive proof is afforded by the shells and corals, or bodies 

 having the perfect shape of shells and corals, and ot other 

 marine exuviae, which are found imbedded in masses of 

 the most solid rock, and often on the tops of very high 

 mountains. This leaves no doubt of the formation of the 

 land under the sea, though it does not determine whe- 

 ther the land, since its formation, has been elevated to 

 its present height, or the sea depressed to its present 

 level. The decision of that question requires other facts 

 to be consulted. 



IV. The instantia clandestina, which is, as it were, 

 opposed to the preceding, and shows some power or 

 quality just as it is beginning to exist, and in its weakest 

 state, :z often very useful in the generalization of facts. 

 Bacon also gave to this the fanciful name of instantia 

 crepusculi. 



An example of this may be given from hydrostaticks. 

 If the suspension of water in capillary tubes be inquired 

 into, it becomes very useful to view that effect when if is 

 least, or when the tube ceases to be capillary, and be- 

 comes a vessel of a large diameter. The column is then 



