Ill 



MAECH. 



PERHAPS the most effective aid to the investigation 

 of natural history which the present age has produced 

 is the invention of the aquarium, and particularly its 

 application to marine forms of life. Depending on that 

 grand principle of organic chemistry, of world-wide 

 prevalence, that the emanations from animals and vege- 

 tables are respectively essential to the continued life 

 each of the other, it was discovered that the relative 

 proportions of number and bulk in which organic 

 beings of the two kinds could healthfully live together 

 was easily determined ; and since the fact that the 

 creatures were inhabitants of water, whether fresh or 

 salt, presented no exception to the universality of the 

 law, they had but to be placed together in a suitable 

 ratio, enclosed in a vessel containing water, and an 

 aquarium was established. Inprovements in the form 

 of the vessel, in the mode of exposing the contents to 

 observation, in the impact of the rays of light, in the 



