We learn that a dreadful fire broke out in Pottsmouth (Portsmouth?), New Hampshire on the 27th ult., which did not cease until nearly a fourth of the town, and the most valuable property, was totally destroyed. The loss, as far as can be ascertained, is computed at upwards of 500,000 dollars. Subscription papers are opened in the cities of New York and Philadelphia for the relief of the unfortunate sufferers by this great calamity.