A BURNING SPEECH. Hon Galusha A. Grow and Hon Schuyler Colfax are in Minnesota. They were the principal speakers at a mass meeting in St Paul last evening, in the theatre. Just as Mr Colfax was drawing his remarks to a close, and while yet the theatre was densely crowded, there was an alarm of fire. The cry was at once taken up, and soon the words “the theatre is on fire!” went up from all parts of the house. A smoke was seen issuing from the rear part of the stage and immediately there was a hurrying for the door. The words, however, that there was “no danger,” “plenty of time,” &c., &c., prevented any confusion, but the audience moved hurriedly and safely out of the door. A few of the more fearful, however, took the short cut and jumped out of the windows. The flames burst up through the rear end of the stage floor and ignited the scenery, and very soon the Thespian temple was all a blaze. In ten minutes from the time the fire was discovered, the whole building was in ruins. How the fire originated is involved in mystery, but from the fact that it was first discovered in the extreme rear end of the building, under the stage, where no fire could accidentally have been dropped, is clear proof that it was the work of an incendiary.