"The number of chapels, steeples, doors and spires may be modified indefinitely, according to the century, the people and the art. Statues, stained glass, rose-windows, arabesques, denticulations, capitals and bas-reliefs are employed according as they are desired. Hence the immense variety in the exterior of structures, within which there dwells such unity and order." The nave here is two hundred and twenty feet long, almost eighty in height, and one hundred and twenty in width, including the side aisles. The walls, which are five feet thick, have fourteen side windows forty feet high, which light softly the galleries and grand aisle. So admirable is the arrangement, that fifteen thousand people can find accommodation and hear perfectly in all parts of the building. On high festivals, such as Christmas or Easter, when the great organ, said to be the finest in America, under the fingers of a master, with full choir and orchestra, rolls out the music of the masses, the senses are enthralled by the magnificence of the harmony. The various altars and mural decorations are beautiful with painting, gilding and carving. In the subdued light, which filters through the stained windows, are found many things of especial sanctity to the faithful. On a column rests an exquisite little statuette of the Virgin, which was a gift from Pope Pius the Ninth, the finely chased and wrought crucifix and the riband attached to it having been worn around the neck of the High Pontiff himself. Directly opposite to it is a statue of St. Peter, a copy of that at Rome. Fifty days indulgence are granted to those who piously kiss this image. Under one altar rest the bones of St. Felix, which were taken from the Catacombs at Rome, and on another is a picture of the Madonna, said to be a copy of one painted by St. Luke. On all the shrines are candlesticks, votive offerings and many other articles of great age, value and veneration. The main altar is exceedingly rich in artistic ornamentation, representing in its design the religious history of the world, and is the only one of the kind in existence. Although the foundation stones of this great pile were laid seventy years ago, this grand anthem in stone has not yet reached its "amen," many additions to it being yet in contemplation. Like many others of earth masterpieces in architecture, it is at once the monument to and the mausoleum of its builder, whose body, according to his dying request, although a Protestant, lies in the vaults beneath his greatest life-work.