May 25, 1857.] PHYSICAL GEOGRAPHY. 413 



above the sea. Here, above all tbe clouds, except a few scirri, 

 which appeared about one day in five, he mounted the five-feet 

 Sheepshanks equatorial, which revealed test objects of three magni- 

 tudes smaller than it had ever shown before. In the apparatus 

 supplied by Prof. Stokes, the increase of black lines was remarkable 

 as the sun's zenith distance increased, and there was a growth of 

 the red end of the spectrum. The dryness was so great, that while 

 the country below was covered by a dense bed of clouds, the ave- 

 rage of the dew point was 40°. The sun's radiation exceeded the 

 graduation of the instruments, the temperature reading 180° -}- x. 

 The moon's radiation became perfectly sensible to Mr. Gassiot's 

 thermo-multiplier, showing it to amount to one-third of the heat of 

 a candle at the distance of 15 feet. 



The second station was at Alta Vista, 10,710 feet above the sea; 

 and there the twelve feet Pattinson equatorial was finally mounted, 

 and by its space-penetrating power, stars of the sixteenth magnitude 

 were easily seen, and the fractions of a second in the distance of 

 double stars were defined. The colour also was observed. Only 

 on one occasion could red prominences in the sun be suspected. 

 Many other branches of observation were included, and minutely 

 reported to the Admiralty. The breaking up of the season, after 

 the middle of September, rendered a hasty retreat necessary, but 

 with the conviction of a yet higher station being desirable in future, 

 if only to get above the persecuting dust, a convenient site was 

 marked at the height of 11,700 feet above the sea, still accessible 

 to mules, if a little money were spent in removing some rugged 

 blocks of lava. 



Specific Gravity of Sea-water. — Our attention was recently called to 

 the condition of the sea- water on the West Coast of Africa, when it 

 was rendered more or less turbid to the distance of many miles from 

 the mouth of the great river Congo or Zaire. Dr. James Campbell, 

 F.R.G.S., of H. M. ship Plumper, observing this phenomenon, had the 

 precaution to collect and send home, with a notice, various samples 

 of sea-water taken at various distances from the shore, noting the 

 day of collection, the latitude and longitude, and the temperature 

 of the water and air at each of these spots. It became therefore a 

 subject of interest to determine, if possible, the nature of the dis- 

 colouring matter, and the relative specific gravity of the water in 

 the diff'erent localities. Mr. Henry M. Witt, of the Government 

 School of Mines, has had the goodness to examine, at my request, 

 these samples of water, and his account of them will be publiKshed in 



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