niPPOLITO SALVIANI. 19 



Natural History, lie remarks, is a science of 

 facts, and the number it comprehends is so great, 

 that no single individual can collect or verify those 

 which belong even to a single department : they 

 can advantageously be studied only by examining 

 all the authors who have WTitten upon them, and 

 by comparing their statements with nature. It is 

 likewise true, that for the profitable examination 

 of these writers, for a just estimate of the degree 

 of confidence to be reposed in each, for the dis- 

 covery of the result of their individual laboui's, and 

 what they derived from those of their predecessors, 

 it is requisite that we should also knoAV the circum- 

 stances in which they worked, the time when they 

 lived, the state in which they found the science, 

 the favouring circumstances in which they \vere 

 placed, both as it regards themselves and their 

 assistants, whether friends, patrons or pupils. These 

 details, arranged in the order of time, and connected 

 by their several links, constitute the history of the 

 science, the necessary basis of any work which 

 would present a general view of the whole. 



Three principal epochs may be recognized in the 

 progress of Ichthyology. Like the other branches 

 of Zoology, it was at first, and for many ages, 

 composed only of detached observations. Aristotle, 

 three hundred years before the present era, began 

 to collect the scattered materials into a system, at 

 first very imperfect; founded upon observations 

 and rules which were scarcely verified, and pecu- 

 liarly destitute of the means whereby one species 



