"The one that has been erected in the Campus Martius has been applied to a singular purpose by the late Emperor Augustus--that of marking the shadows projected by the sun, and so measuring the length of the days and nights. With this object, a stone pavement was laid, the extreme length of which corresponded exactly with the length of the shadow thrown by the obelisk at the sixth hour on the day of the winter solstice. After this period the shadow would go on day by day gradually decreasing, and then again would as gradually increase, correspondingly with certain lines of brass that were inserted in the stone--a device well deserving to be known, and due to the ingenuity of Facundus Novus, the mathematician. Upon the apex of the obelisk he placed a gilded ball, in order that the shadow of the summit might be condensed and agglomerated, and so prevent the shadow of the apex itself from running to a fine point of enormous extent, the plan being first suggested to him, it is said, by the shadow that is projected by the human head. For nearly the last thirty years, however, the observations derived from this dial have been found not to agree,--whether it is that the sun itself has changed its course, in consequence of some derangement of the heavenly system; or whether that the whole earth has been in some degree displaced from its centre--a thing that, I have heard say, has been remarked in other places as well; or whether that some earthquake, confined to this city only, has wrenched the dial from its original position; or whether it is that, in consequence of the inundations of the Tiber, the foundations of the mass have subsided, in spite of the general assertion that they are sunk as deep into the earth as the obelisk erected upon them is high." _Regaining the Corso, the first turning on the right, Via Pietra, leads into the_ PIAZZA DI PIETRA, in which are the ruins of THE TEMPLE OF NEPTUNE. Eleven Corinthian columns, which formed a part of one side of the temple, still stand, forming the entrance into a building once used as a custom-house. They are 42½ feet high and 4½ feet in diameter, supporting an architrave of marble which has been recently restored. In the interior are some immense blocks of marble which formed part of the vaulting. The temple, with the Portico of the Argonauts which surrounded it, was erected by Agrippa. It is now used as a chamber of commerce. [Illustration: TEMPLE OF NEPTUNE.] _Continuing our ramble along the Corso, on the right_ is the PALAZZO SIMONETTI, on the left the PALAZZO SCIARRA. The pictures here have not been shown to the public for some years. Beyond, _standing back_, is the CHURCH OF S. MARCELLO, containing the celebrated cherubs of Pierino del Vaga, the most exquisite things ever done in fresco. The tomb of Cardinal Weld is also here. Rienzi's body was hung up by the feet for two days in front of this church. THE CHURCH OF S. MARIA IN VIA LATA