MARS AND VENUS. 



SANTIAGO OBSERVATIONS. 



INTRODUCTION. 



DESCRIPTION OF THE OBSERVATORY. 



The rotary observatory of the astronomical expedition occupied a terrace constructed 175 feet 

 above the streets of Santiago, and on the northern slope of Santa Lucia. Its elevation above 

 the sea is 1,940 feet. The terrace was formed partially by breaking down crags of the rock com- 

 posing the hill, and partially by building a dry wall thirty feet high, upon a projecting ledge, 

 from the west side. . Between the wall and slope of the hill, the space perhaps six feet wide at 

 top was filled with fragments of porphyry and loose earth, to which solidity was given by 

 pouring in water during the progress of the work. An artificial surface was gained by these 

 operations forty feet in extent from east to west, and twenty-five feet wide from north to south. 

 As this terrace is nearly ten feet more elevated than that on which the observatory building for 

 the meridian circle is erected, a flight of steps was made from one to the other by using the 

 columnar strata of the hill. The rotary observatory occupies the western side of its terrace, 

 with only a narrow pathway between it and the face of the artificial wall. 



The pier for the telescope was first built. On a mass of masonry, five feet in diameter and 

 two and a half feet high, there are secured four capping-stones of red porphyry that form an 

 octagon seven inches thick and inscribed in a circle 6.5 feet in diameter. No single stone 

 of such dimensions could have been quarried by the artisans of Santiago, and if obtainable, 

 could not have been raised to the observatory without sending to Valparaiso for machinery. 

 The base of the masonry was the native rock, and the bed and joints of the cap-stone were 

 filled in with a grouting of hydraulic lime. A foundation of masonry, fifteen feet in diameter, 

 and rather more than a foot in height above the surface, was built on the rock, in situ, sur- 

 rounding the pier, to receive the sill of the observatory. 



The sill, formed from circular segments of one and a half inch plank, five and a half feet 

 long, is put together so as to break joints, and rests immediately on wedges laid on the masonry 

 diametrically. A grooved cast-iron rail is secured by screw-bolts and nuts near the centre of 

 its upper surface, and the level of the sill is perfected by means of the wedges. The curb is 

 formed in the same manner, but of rather stronger wood, and it is rendered more inflexible by 

 the manner in which the corresponding grooved rail is secured to its under side. It rests on 

 six 24-pounder cannon balls. Both the curb and sill are composed of two thicknesses of plank. 

 The frame-work of the building, supported on the former, is of light and well-seasoned yellow 

 pine, and the weather-boards are of white pine, tongued and grooved together, and fastened to 

 the frame by screws. The height to the eaves is eight feet. The roof is a cone, having for its 

 apex a tin cap, hung by one edge on long hinges, and which, when closed, laps two inches over 

 the wood-work all round. The aperture covered by the cap is two feet in diameter ; the width 

 of the door in the inclined roof twenty inches. An upright, that passes through the roof and 



