VINDICATION OF THE FUGITIVE SLAVE LAW IN OTTAWA.- An instance of the vindication of the Fugitive Slave law has just occurred in Ottawa, which shows that even in the most northern part of this State, in immediate contiguity to the depot of the underground railroad, juries can be found to carry out constitutional laws without regard to prejudice. The case referred to is that of the United States against John Hossack and others, the defendants having, in October last, rescued a fugitive from Missouri from the hands of an officer after he had been delivered upon a warrant from a United States commissioner. The defendants were duly convicted by a jury, and were called up for sentence at the present term of the United States District Court. Hossack, in answer to the question why sentence should not be passed, it appears, read a paper, in which he claimed exemption from punishment on the ground that the Fugitive Slave law was unconstitutional, and protesting against the action of the court. Judge Drummond, instead of disregarding such a plea, as he might have done, and proceeding to sentence the prisoner forthwith, entered into an elaborate reply to Hossack's protest, and ably vindicated the constitutionality of the law and the jurisdiction of the court. This was an unusual proceeding; but it may have a good effect upon those violators of the law who lean upon the weak support of their own interpretation of the law as a protection against punishment, and deliberately become criminals in the fallacious hope that what they denominate conscience will screen them from the just penalty of crime. Hossack was fined a hundred dollars and sent to prison for ten days - a very mild punishment considering the nature of the offence.