place by machinery. It can be tinted to the taste of the purchaser; but, as a rule, a tintless crystal is preferred. The entire work of building a large house, from the foundation to the finishing and removal of the metallic frames, occupies from half-a-dozen to eighteen workmen from four to eight days. This, like most other labour in Mars, goes on continuously; the electric lamps, raised to a great height on hollow metallic poles, affording by night a very sufficient substitute for the light of the sun. All work is done by three relays of artisans; the first set working from noon till evening, the next from evening till morning, and the third from morning to noon.
The Martial day, which consists of about twenty-four hours forty minutes of our time, is divided in a somewhat peculiar manner. The two-hour periods, of which "mean" sunrise and sunset are severally the middle points, are respectively called the morning and evening zydau. Two periods of the same length before and after noon and midnight are distinguished as the first and second dark, the first and second mid-day zyda. There remain four intervals of three hours each, popularly described as the sleeping, waking, after-sunrise, and fore-sunset zyda respectively. This is the popular reckoning, and that marked upon the instruments which record time for ordinary purposes, and by these the meals and other industrial and domestic epochs are fixed. But for purposes of exact calculation, the day, beginning an hour before mean sunrise, is distributed into twelve periods, or antoi, of a little more than two terrestrial hours each. These again are subdivided by twelve into periods of a little more than 10m., 50s., 212s., and 524s respectively; but of these the second and last are alone em
