To the original bequest Mr. William B. Astor has since added a large conveyance of real estate, and the institution is nearly double its original size. Speaking of Mr. William B. Astor, we may be led to a few references of a personal nature. As the ordinary street-passenger is traversing Prince street, he is not likely to be struck by any of its surroundings. The street itself is but of third-rate character, and the houses are but of a common stamp. Near Broadway, however, one may notice a small brick office, neatly built, of one story, with gable to the street, but with doors and windows closed, and the whole appearance one of security. Near the door may be seen a little sign which reads thus: 'Entrance next door: office hours from nine to three.' The next door, to which we are referred, is a plain three-story brick dwelling, with no name on the door, and might be taken for the residence of some well-to-do old-fashioned family. Hence one is quite startled to find that this is the headquarters of the chief capitalist of America. Entering the street-door, one will find himself in a small vestibule, neatly floored with checkered oil-cloth, and opening a door on his left, he will enter a well-lighted front-room, destitute of any furniture but a counting-house desk and a few chairs. At this desk stands an accountant (or perhaps two) working at a set of books, and evidently enjoying an easy berth. He will answer all ordinary inquiries, will do the duty of refusing charitable demands, and will attend to any thing in the ordinary run of business; but if one has any thing special on hand, he will point to a door opening into a rear office. This apartment is of moderate size and of simple furniture. On the table are a few books, and on opening one of them, which appears well thumbed, it will be found to contain maps of plots of city property, carefully and elegantly executed, and embracing the boundaries of an enormous estate. Seated by the table may generally be seen a stout-built man with large and unattractive features, and upon the whole an ordinary face. He is plainly dressed, and has a somewhat care-worn look, and appears to be fifty or sixty years of age. One naturally feels (that is, if he be a poor man) that it is quite a rare thing to address a capitalist, and especially when that capitalist is the representative, say of twenty-five millions of dollars. Such, at least, was our experience at our first interview with William B. Astor.