The demonstrations in the lower part of the city excited the greatest anxiety about the Government buildings in that section--the Custom House and Sub-treasury were tempting prizes to the rioters. General Sandford, commanding the city military, had sent such force as he could collect early in the day to the arsenal, to defend it; for, should the mob once get possession of the arms and ammunition stored there, no one could tell what the end would be. United States troops also were placed in Government buildings to protect them. Almost the last act of the mob this evening was the burning of Postmaster Wakeman's house, in Eighty-sixth Street. Mrs. Wakeman was noted for her kindness to the poor and wretched, who now repaid her by sacking and burning her house. The precinct station near by was also destroyed. In the meanwhile, an event happened which threatened to disarrange all the plans that had been laid. Military etiquette often overrides the public good, and here, at this critical moment, General Wool chose to consider that, as General Sandford was Major-general, though not in the United States service, he, therefore, ranked Brigadier-general Brown of the regular army, and required him to act under the other's orders. This, Brown promptly refused to do, and asked to be relieved, telling General Wool that such a proceeding was an unheard-of thing. That he was right the order below will show [Footnote: [GENERAL ORDER No. 36.] WAR DEPARTMENT, _Adjutant-general's Office, Washington_, April 7th, 1863. 6. The military commander's duties in reference to all troops and enlisted men who happen to serve within the limits of his command will be _precisely those of a commanding officer of a military post_. The duties of military commanders above defined, will devolve in the _City of New York, and the military posts in that vicinity_, on Brevet Brigadier-general H. Brown, Colonel Fifth U. S. Artillery.