Doctor Powell, well known as an able and enthusiastic advocate of phrenology, at present lecturing in the city, confident in the truths of the science, pronounces upon character agreeably to the external configuration of the crania with fearlessness the most perfect. Since his arrival here, we have known him examine three different crania, which were presented to him for the purpose of testing the truth of phrenological doctrines. The two first were handed him by Mr. Dorfeuille, the intelligent proprietor of the Western Museum. The first one, which Doctor Powell saw, he immediately perceived the preponderance of the vicious propensities over the moral sentiments, and unhesitatingly said, its owner, according to the laws of the land, deserved hanging, if he were not actually executed. The second one was presented, and he forthwith pronounced its possessor equally bad with the former, although unpossessed of his recklessness, and greatly more cautious and secretive. Mr. Dorfeuille then stated, that the sculls belonged to two negro fellows who were executed some years ago in New Orleans, and whose heads after execution were stuck on pikes. The first fellow was notoriously vile and daring; the other was more shy, and against him no absolute proof could be brought; but he was convicted on evidence so strong as to defy the resistance of the judgment. The delineation of their characters upon the principles of phrenology he acknowledged to be most complete. On last Monday evening, professor Cobb, of the medical college, sent a cranium to Doctor Powell for examination, in the presence of his class. He took it up and pronounced its prominent developments to be those of combativeness, destructiveness, secretiveness, acquisitiveness: he said that each of these propensities might have manifested itself singly; but the probability was that they co-operated, and the consequence was, that their subject was addicted to robbery on the highways, and was highly combative. After he had finished his examination, he called on professor Cobb to state what he knew of the character of the individual. He arose, and said that, so far as he was aware, the lecturer had determined truly. The skull had belonged to a Spaniard confined under suspicion of piracy, in the Cincinnati jail last winter, and who, while there, had committed suicide, and thus escaped trial.--An examination of his body proved what the lecturer had said in regard to his combativeness, as it was scarified in many places. We have since understood, that this Spaniard was arrested for attempting to stab a person in the street, and while in confinement, was recognized as a pirate, and, in order to avoid the consequences of a trial on the charge of piracy, he had cut the principal arteries of both arms, and died from the wounds thus inflicted. Dr. Powell had no intimation of the character of either of the individuals, which he portrayed with such exactness; but relied solely on phrenological science.