XL INTRODUCTION. 



removed from the mirror and suspended horizontally, its bulb was wrapped with muslin and 

 kept moistened. It thus served as a registering thermometer for the minimum temperature 

 of evaporation, and was placed beside the psychrometer. Solar : There were two registering 

 thermometers, with blackened bulbs, made for the Expedition by Mr. Barrow; but one of them 

 was broken in the transportation, and the second was accidentally destroyed within a day or two 

 after unpacking it. 



Winds. A vane, with an attached pressiire-plate, communicating motion to a fine gradu- 

 ated chain that led into the office, was erected on the roof above, but it proved worse than use- 

 less. It has been stated that the position of our residence was unfavorable for accurate estima- 

 tion of the direction of the winds ; indeed, there is probably no point of the city of Santiago 

 where atmospheric currents are not influenced by the hills already named, and two others just 

 without the northern and northwestern limits. Here the vane was whirled to every point of 

 the compass but the true one ; and therefore, during the day, the direction was taken from that 

 of the flag hoisted at the castle on the western escarpment of Santa Lucia, the line in which 

 smoke travelled, or, from the plane in which the slender poplars near us were inclined. At night, 

 when these objects were no longer visible, there was even greater uncertainty, but then the cur- 

 rents were invariably both light and from the Andes. As there was no anemometer, (the pres- 

 sure-plate failing with the vane,) the relative force is entirely derived from estimate of the effect 

 of the wind on surrounding objects, denoting a calm, 1 a very light breeze, and so on to 10 

 a strong gale. 



Clouds. The amount of sky hidden by clouds is merely a naked-eye estimate, representing 

 cloudless, and 10 entire obscuration. This is not strictly true of the first symbol in all cases, for 

 during summer, and a portion of the spring and autumn, so long as the day-breeze continues, a 

 low bank of heavy cumuli almost invariably remains over the Andes E.N.E. of the city, and 

 these are not mentioned in the column "clouds" unless the apparent elevation and mass are 

 remarkable. However, the fact that such clouds were perceptible is duly stated in a side-note. As 

 no such clouds are regularly formed at the same time above the summits of the western cordil- 

 leras, the phenomenon is the more striking. The nomenclature of Howard has been adopted, 

 C., K., S.,N., being symbols for the forms of clouds which he denominates cirrus, cumulus, stratus, 

 nimbus ; and the double letters C. S., C. K., &c., their combinations to indicate cirro-stratus, cirro- 

 cumulus, &c. 



Rain-gauge. The rain-gauge was made of stout sheet-copper, by Messrs. Pike & Son, of 

 New York. It was a simple cylinder-gauge, six inches in diameter, soldered to an inverted 

 cone of six inches perpendicular height. There was an aperture at the apex of the cone through 

 which the rain-water passed to a receiving bottle as fast as it descended, the gauge being main- 

 tained perpendicularly and firmly on the bottle by a deep flange that clasped the neck. The 

 instrument was placed upon the ground within our premises, and the quantity of water collected 

 was measured at midnight, or oftener, in a graduated glass cylinder of about one inch diame- 

 ter. As the ratio of the receiving to that of the measuring cylinder was as more than forty to 

 one, very small quantities could be determined with accuracy. 



Personnel. Until the 13th September., 1850, the meteorological journal was in charge of 

 Passed Midshipman H. C. Hunter and captain's clerk E. K. Smith, each of whom alternately 

 made the records during twenty-four hours, commencing with the observations at 6 A. M. 

 An accident prevented the former from performing his portion of the duty between January 20 

 and March 28, 1850 ; and after September 13 of that year, when he returned to the United States, 

 Mr. Smith alone was responsible. Every member of the Expedition was expected to enter 

 remarkable phenomena that occurred under his notice, and many such will be found with initials 

 annexed to designate the individual. 



The tabular results were computed by Assistant E. F. Phelps. 



