Physical Observations, Sfc. 239 



were the two following : The first, was made in the morning of the 

 24th of August, in the Gulf Stream, in latitude 37° 46' N., and 

 longitude 68° 05' W., in order to determine whether its waters were 

 in motion at any considerable depth. In sending down the instru- 

 ment to the depth of one hundred fathoms, it indicated a tempera- 

 ture of 80° F., while the water at the surface was 82°, and the at- 

 mosphere in the shade 78°, a conclusive evidence that its waters 

 were in motion at that depth. The second was made in the eve- 

 ning of the 10th of October, near the equator, in longitude 28° 36' 

 W., where the instrument gave a temperature of 64° at the depth 

 of one hundred and seventy fathoms, while the surface temperature, 

 and that of the air in the shade were each 78°. In the latter ex- 

 periment, the water brought up in the valved instrument, was high- 

 ly charged with gas, which, when exposed to the atmosphere, made 

 its escape by a slight effervescence. 



Evaporating State of the Atmosphere. — This was imperfectly 

 determined by noting the descent of the mercury in the thermome- 

 ter, after plunging it into water, and then exposing it a short time 

 to the rays of the sun in the open air. Then the number of de- 

 grees that the mercury descended below the temperature of the air 

 in the sun, was noted, and was considered as an index to the ap- 

 proximate dryness or humidity of the atmosphere. 



Hygroscopical State of the Atmosphere. — This was determined 

 by an accurate hygrometer, constructed after that of M. de Saus- 

 sure, and was placed under the break of the poop of the ship for ob- 

 servation during the passage. 



Barometrical State of the Atmosphere. — The instrument used 

 for this purpose, was a common marine barometer, suspended in the 

 large cabin of the ship, which was kept well ventilated during the 

 time of observation. 



Intensity of the Light of the Sun. — This was determined by a 

 good photometer, constructed after that of Professor Leslie, which 

 was exposed to the light, on the poop of the ship, about one min- 

 ute at each observation. The instrument when taken directly from 

 the dark, invariably stood at 4°, and when exposed to the light of 

 the full moon, it stood at 10°. 



Color of the Sky. — The instrument employed for this purpose, 

 was a cyanometer, graduated after that of M. de Saussure. The 

 observations were always made near the horizon, and about the ze- 

 nith, except when the sun was in the latter situation, then the ze- 

 nith observations were taken about 15° from the sun. 



