In the meantime, General Pearson, fearing that the majority of the men in these regiments sympathized with the strikers, telegraphed Adjutant General Latta to that effect, and suggested that troops from Philadelphia should be sent on, and gave it as his opinion that two thousand troops would be needed to disperse the mob, as it was now (six thirty-five, P.M.,) very large (four thousand to five thousand men) and increasing hourly. General Latta at once telegraphed Major General Brinton, commanding the First division of the National Guard, at Philadelphia, to get his command ready to move to Pittsburgh. General Brinton received this order in the evening, and at two o'clock on the morning of the 21st he had six hundred men at the railroad depot ready to start. At Harrisburg, General Brinton received some ammunition and two Gatling guns, and reached Pittsburgh at one, P.M., and reported to General Latta at the Union depot hotel, and there distributed twenty rounds of ammunition to his men. In order to understand the situation of things and the future movements of the troops, a description of the depots, buildings, tracks, and surroundings of the Pennsylvania railroad property at Pittsburgh is here necessary. The Union depot was situated between Seventh and Eighth streets, and from this place the line of the railroad ran eastwardly, at the foot of a steep bluff, from one hundred and fifty to two hundred feet high on the right, and with Liberty street on the left. There were a great number of tracks running side by side out to and some distance beyond Twenty-eighth street, with numerous switches in order that the tracks might be used conveniently, and many of these tracks were filled with cars, passenger and baggage cars near the depot, and freight cars further out. The outer depot, lower round house, machine shops, &c., were situated at and near Twenty-sixth street, about a mile from the Union depot, some other shops were scattered along there to Twenty-eighth street, near which street was what was called the upper round-house. From Twenty-eighth street down to the Union depot the tracks were several feet higher than Liberty street, and a strong wall was built up at the side of Liberty street to support the embankment and keep it from caving into the street. At Twenty-eighth street there was a crossing much used, the bluff not being as steep or as high here as it is further down, and the hill is ascended by a diagonal road or path from the crossing.