ON THREE BALLOON ASCENTS IN 1864 AND 1865. 149 



earth, nearly so brilliant as it always is on rising above the lower atmosphere, 

 although I have examined the solar spectrum many hundreds of times on the 

 finest days. The spectrum, when viewed from above, is perfect with a much 

 narrower opening of the slit than it is on the ground, and consequently lines 

 can be resolved clearly which cannot be seen from the earth. 



A very delicate blackencd-bulb thermometer, placed with its bulb near 

 to the carefully screened bulb for temperature of the air, in the first of these 

 three ascents, generally read the same as that for the temperature of the air, 

 occasionally read lower, and never during the ascent read more than 1° in 

 excess. The same results were observed in the ascent on December 30tb. 

 In the ascent on February 27 it generally read the same; but at times, 

 when the sun was shining the brightest, it read from 2° to 3° higher than its 

 shaded neighbour. 



No tinge of ozone was shown on any test-paper spread freely about on the 

 rigging in any of these journeys. 



§ 3. Description of the Table of Observations. 



All the meteorological observations taken during the ascents are contained 

 in Table I. 



Column 1 contains the times at which the observations were made. Column 

 2 contains observations of the siphon barometer corrected for temperature and 

 index error. Column 3 contains the readings of the thermometer attached 

 to the barometer. Column 4 contains the readings of an aneroid barometer. 

 Column 5 contains the height above the level of the sea, as reduced from the 

 barometric readings in column 2 on the days the siphon barometer was used, 

 and from column 4 on other days, by the formula of Baily, checked at inter- 

 vals by that of Laplace, which is as follows : — - 



z= 1 „ g (i,) x6 o 158 ( 1+ ^r«) (l+ „,o 283 rc„ s2 L)( 1+ lg|l), 



where Z is the height required, and h, Ji', t and t' the height of the barometer, 

 corrected for temperature, and the temperature of the air at the lower and 

 upper stations respectively, L the latitude. The temperature of the air for the 

 position of the balloon has been derived from the readings in column 10, 

 when such have been taken, otherwise from column 6. Columns 6 to 9 

 contain the observations with the dry- and wet-bulb thermometers free, 

 and the deduced dew-point. Column 10 contains the readings of a 

 gridiron thermometer. Columns 11 to 14 contain the observations with 

 the dry- and wet-bulb thermometers aspirated, and the deduced dew- 

 point. Columns 15 and 16 contain the direct dew-point observations with 

 Daniell's and Kcgnault's hygrometers. "When numbers are entered in 

 columns 15 and 16 with " no dew " affixed to them, it is meant that the 

 temperature of the hygrometer has been lowered to the degree stated, but that 

 no dew has been deposited. Column 17 contains the readings of a very de- 

 licate blackened-biub thermometer fully exposed to the sun's rays. 



The Astronomer Eoyal had observations made every ten minutes at the 

 Eoyal Observatory, Greenwich, on the days of ascent, by Mr. Nash of the Mag- 

 netical and Meteorological Department. 



The height of Greenwich barometer- cistern above the mean sea-level is 

 159 feet. 



