The “Boston Atlas” says the following fact may be useful, not only in guarding against a similar occurrence, but in suggesting one among many causes of fire, which are, nn-doubtedly, often wrongly attributed to incen diarism :—A tew days since, a gentleman in the vicinity ot Boston observed that the tas sel to the shade of his chamber window was badly burned, and in a manner which gave no indication of the cause. He failed in his in quiries, and no person in the house could give him any information. A morning or two af ter, the domestic who was attending to the room, ran down in haste, exclaiming that the chamber window was on fire. An examina tion explained the mystery. In front of the window which looked easterly, stood a sha ving glass affixed to a movable stand. A magnifying glass on the back reflected the rays of the sun, bringingthem to a focus or. the window, and whenever they struck on wood they burned into it, charring the frame in many places. A piece of paper placed against the window was set on fire, and, in deed, the heat was so intense that it instantly burned whatever it touched. When first dis covered the frame of the window was blazing. Had the fire extended, it is not probable that the origin of it would have been discovered, and it would have been placed among those incomprehensible causes which can find no other solution than wilful mischief. A planter near Franklin, La., has gathered this season eleven hundred and seventy-seven bushels of sweet potatoes from three acres ol land—and left behind, he says, enough to fat ten about forty hogs.