XXXYI INTRODUCTION. 



INSTRUMENTS AND OBSERVATIONS. 



The meteorological observations were all made at our residence, whose situation near Santa 

 Lucia has already been mentioned. Its location was unfavorable for the observation of accu- 

 rate thermometric changes, no less than for proper appreciation of the course of the wind. 

 Being in a sort of gorge between Santa Lucia and San Cristoval spur, and near the river 

 Mapocho, it was subject to greater amounts of radiant heat and to inflections of the atmo- 

 spheric current by day, whilst the proximity of a rapid volume of snow-water most probably 

 influenced the night temperature. 



During the earlier observations all the thermometers were arranged under an open corridor 

 of the ground-floor, which faced a small court-yard near the centre of the dwelling; but it was 

 soon found that the heat radiated from the paved surface was sensibly too great, and they were 

 removed to a balcony on the south front of the second story. 



BAROMETER. 



The barometer was made at the office of the United States Coast Survey, after the form of 

 Mr. F. R. Hassler, described in Senate document No. 225, 2d session 27^11 Congress, (April, 

 1842.) The tube is sixty -five (0.65 inch) hundred ths of an inch in its internal diameter, and was 

 suspended from a strong bracket in an angle of the wall. A narrow brass ferrule, furnished at 

 top with a hinged loop, is made to press the tube closely by a pinching screw at the side of the 

 ferrule, and the latter is prevented from binding unequally by a bit of chamois leather inserted 

 between it and the glass. To the lower end of the tube there is cemented a steel ferrule, made 

 with two flat prongs diametrically opposite each other, and wlych extend half an inch below 

 the glass. Each prong or leg has a slit intended for the passage of a packing wedge of the 

 same metal, and the tube is closed by a steel plate furnished with a leather cushion, this last 

 pressed somewhat into the tube by means of the wedge. Only the lower ferrule is permanently 

 secured to the tube. 



The cistern used was a glazed earthenware cup, sufficiently large to permit insertion of the 

 fingers for removal of the packing wedge and plate when the lower extremity of the tube hung 

 within it. It rested on a little shelf secured in an angle of the wall, and at twenty feet above 

 the ground. 



A stout plate of brass, firmly screwed to the top of the bracket, from which the tube is sus- 

 pended, has two apertures one oblong, the other circular and the two about one inch apart. 

 The former freely admits a flat screw having a hook at its lower extremity, that has motion in a 

 horizontal plane, the upper or screw portion passing through a milled-head screw, by which it 

 may be moved vertically. When the loop of the upper ferrule is hung upon the hook, the 

 barometer tube assumes a vertical line by its own gravity. 



The scale for measuring the height of the column of mercury hangs beside and to the left of 

 the tube. It consists of a steel rod, one-fourth of an inch in diameter, with a very fine screw 

 cut upon its upper end, and a zero mark perhaps half an inch from the lower extremity. The 

 screw end passes freely through the second aperture in the brass bracket-plate, where it is held 

 by a thumb-screw, and the lower end slides easily through a light ivory float that rests on the 

 surface of the mercury in the cistern. A silvered brass scale, divided to tenths of an inch, from 

 twenty-five inches to thirty-one inches, is permanently secured to the upper extremity of the 

 steel rod, so that one edge of the scale is beside the barometer tube. The scale is furnished 

 with a vernier reading to .002 inch. It carries a slip of brass that partially encircles the tube, 

 and is moved by a tangent screw. As the lower edges of the brass slip are in the same hori- 

 zontal plane, if the eye also be placed in that plane it estimates very accurately when the 

 edges form a tangent to the convex surface of the mercury in the tube. By construction, the 



