322 Mr Becquerel on the Relations of Natural Philosophy 



what has been witnessed by M. Brechet and myself on the 

 Brenta in September 1835. 



Finally, we shall direct attention for a moment to the very 

 gradual operations which are continually going forward at the 

 surface and in the interior of the earth, and to the production of 

 which all the powers of nature, such as heat, light, electricity, 

 affinities, capillary attraction, and even organic agencies contri- 

 bute. Up to the present time these have engaged but little at- 

 tention, because we were not acquainted with all the agencies 

 which co-operated in their development. In examining for ex- 

 ample the antique bronze medals, which have been converted 

 into protoxide of copper, without the form having undergone any- 

 other change than an augmentation of volume, all that used to 

 be stated concerning this kind of metamorphosis was, that it was 

 the consequence of a kind of cementation. Now-a-days we pro- 

 ceed farther ; other analogous facts are produced, and it is at 

 the same time shewn, that nature must employ agencies similar 

 to those which had formerly been used. Such is the power of 

 these agencies, that by acting slowly they lead to the formation 

 of a great number of natural products, and in the very organs 

 and tissues of animals and vegetables accomplish the formation 

 of inorganic compounds, which are sometimes deposited in regu- 

 lar crystals, as we have an example in the eggs of the garden 

 snail, whose external covering is internally skodded with crystals 

 of calcareous spar, as regular and transparent as those rhomboids 

 of Iceland spar which form the ornamental specimens of our 

 mineralogical museums.' 



Might we not then, it may be enquired, by the help of their 

 slow and gradual operations, obtain an idea of the epochs in 

 which have occurred some of the great catastrophes, which on 

 different occasions have broken up the surface of the globe r* It 

 is known that certain rocks, and among others, some kinds of 

 granites, are daily undergoing decomposition ; this operation 

 taking place from the surface of the earth towards the interior, 

 it cannot be doubted is the result of atmospheric influence ; 

 and as its progress is easily traced in ground that is broken up 

 by man's agency, and in detached blocks, it is possible to esta- 

 blish a relation between what has passed during a determinate 

 number of ages, and the effects produced since tlie commence- 



