INTRODUCTION. j x 



often noticed by others, I have nowhere found them alluded to. The 

 direction from which the wind came, in the instance referred to, was 

 northeast, and so brisk as to carry the ship onward at the rate of 

 seven knots. 



One of the phenomena met with on this passage was the red misty 

 haze so prevalent in this track. The state of the meteorological in- 

 struments under which it occurred was as follows, viz. : barometer 

 reduced to 32, 3O020 inches ; temperature of the air, 78 ; tempe- 

 rature of the water, 82; degree of moisture, '706. Wind from 

 the northeast to east-northeast, light and clear over head. During 

 the continuance of the mist a heavy shower occurred, which lasted 

 for an hour ; on its cessation, the dew-point was found at its former 

 standing, but the temperature of the air had fallen 3. I was at first 

 inclined to believe this phenomenon was the result of the difference of 

 temperature between the air and water, but as I afterwards observed 

 the same haze when there was little or no difference noticed, though 

 the trials were repeatedly made, I cannot impute it to such a cause. 

 The most remarkable circumstance accompanying this mist or haze is 

 its red colour. That which occurred at Porto Praya had a great resem- 

 blance to the " dry fogs;" no particles of matter were observed floating 

 in the atmosphere to produce the red colour. During its continuance 

 the sky is clear, and cirrus clouds are often visible, but the horizon is 

 at all times ill-defined and much obscured; objects are quite indistinct 

 and apparently diminished in size, the effect of the red mist being en- 

 tirely the reverse of what takes place in fog. The cause of this pheno- 

 menon, it appears to me, is to be found in the intermingling of currents 

 of air of different temperatures in the higher atmosphere, producing 

 condensation, which descends, and passing through strata both warmer 

 and drier become again absorbed; hence no deposition takes place, 

 and whilst this condensation and absorption are going on, the pheno- 

 menon is seen. That this is the case I think is proved by the 

 state of the mast-head thermometer, it being invariably found to 

 be some two to five degrees lower than that on deck during the con- 

 tinuance of these mists. The red appearance I think may be accounted 

 for by the refraction and reflection of light : as the sun attains the 

 zenith the reddish tint becomes deeper, but is variable according to 

 ,the angle in which the light falls ; in places it is of a lighter hue, and 

 frequently assumes a patched or mottled appearance. At nightfall 

 the same phenomenon takes place, but then there is a deposition 

 which assumes all the appearances of dew, but totally distinct as 



3 



