between the smaller towers, being illuminated by the rising or setting sun, were for the solstices, and the towers on the east answered to those on the west, at the winter or at the summer solstice. In order to verify the event the Inca placed himself in a convenient spot, whence he watched whether the sun rose or set between the two small towers on the east and on the west, and thus the most skilled of the Indians found the astrology of their solstices.
This description, equally naïve and unintelligible, requires some explanation. The towers and turrets went by fours, two large and two small, and there were two systems, intended for the observation, by one system of the winter solstice, by the other of the summer solstice. In position and relative distances they were so arranged that when the sun reached the tropic of Cancer the shadow cast by the northeastern turret was exactly tangential, at the moment of sunrise, to the southern face of the northwestern turret, and at the same time hid the sun from the amantas on observation in the corresponding tower; and vice versa at the moment of sunset. As the sky might be cloudy at sunrise, the astronomers posted to observe the setting sun replaced, confirmed, or rectified, when necessary, the determinations of the morning. The southern turrets were used in the system of observatories for the summer solstice.
Montesinos gives another version which seems different when taken literally, but substantially confirms the former. He relates that the Inca Capac Raymi assembled his learned men and astronomers to find the solstices. "There was a kind of solar quadrant formed by shadows, and with it they knew what day was long and what other was short, and at what time the sun went toward the tropics and returned from them. I saw four very ancient walls on a hill, and a son of the country affirmed to me that this building had served the ancient Indians as a clock." Though precise for that time and place, and quite original, no account has been taken in this method of the change in the obliquity of the ecliptic, forty-eight seconds a year, according to Delambre, the effect of which upon the azimuth is very sensible in those latitudes. Houzeau says that the Incas had no idea of this displacement; that they observed the June solstice only, and that the continued observations of the amantas proved the absence of a solar calendar. It is very possible that the Incas perceived that their observatory system finally became useless, and that, without stopping to inquire into the reason, they constructed new ones. There is no doubt that the Incas recognized the movement of the ecliptic some time before the other people of the Old World, but without
- Garcilaso, Book II, chap, xxiii.