At Reading, on Saturday, July 21st, the idle men began to gather in small bodies and talk of strikes, and showed a disposition to interfere with railroad property, but no overt act was committed until Sunday the 22d. The mob at this place was composed primarily of discharged employés of the Philadelphia and Reading Railroad Company, who had been discharged in the month of April preceding. The officers of that road learning that the society called the Brotherhood of Locomotive Engineers intended to make the company trouble, commenced preparing for it, and when in April the engineers demanded an advance in wages of twenty per centum, they were notified that any person who belonged to the brotherhood could not remain in the employ of the company unless he severed his connection with that society, and that, as the society was a beneficial one, and had a fund for its members to draw on in ease of sickness, the company would establish such a fund for its engineers. In consequence of this demand, and the circular of the company, some four hundred engineers, firemen, and brakemen left the service of the company, whose places were filled by promoting firemen and hiring new men, and those coming from other roads who held certificates of competency and good behavior. Many of these men who left the employ of the company had remained in and about Reading, and on hearing of the riots at Pittsburgh, thought it would be a good time to take their revenge on the Philadelphia and Reading Railroad Company, and these, with other idle men, composed the nucleus of the mob, and were, as in other places, soon joined by all the tramps and criminals in the vicinity. None of the regular employés of the railroad company struck at that time, nor were they engaged in the riots. On Sunday trains were interfered with near the depot, and one or two cars burned, and on Sunday night, the 22d, the Lebanon Valley railroad bridge, which is a very high one, crossing the Schuylkill at Reading, and costing a large sum of money, was burned. On the evening of July 22d, Adjutant General Latta telegraphed to Major General William J. Bolton, commanding the Second division National Guard, with head-quarters at Norristown, to concentrate the Sixteenth regiment, under arms, at once at Norristown, and the Fourth regiment, at Allentown, which was done as soon as possible, and the Fourth regiment, General Reeder, reported on the morning of the 23d, that all the companies were in hand except company A, which was in the hands of the mob at Reading.