temperature of the ocean and atmosphere , &c. 291 
presents itself when a cold wind blows, viz. the south-east. 
This wind must condense the aqueous vapour rising from the 
warm current, and carry it towards the land. During the 
short stay we made at the Cape, I once had an opportunity 
of seeing the mist advancing ; it came rapidly over the sur- 
face of the sea, which it entirely concealed, whilst the air 
above was perfectly clear ; it soon reached the land, spread 
along the coast gradually, ascended the mountain, and there 
remained almost stationary, enveloping the summit, some- 
times encreasing and descending on the opposite side over- 
hanging Cape Town, and sometimes diminishing and retreat- 
ing. That it should remain so nearly stationary on the top 
of Table Hill, whilst the south-east wind continues, is not 
surprising, considering the height of this hill, 3582 feet above 
the level of the sea, its precipitous sides, and the extensive 
surface of its top ; nor is it strange, that it should rarely 
descend, except when the wind blows hard, taking into 
account the situation of the ground beneath, sheltered and 
warm, and the site of a large town, from which a current of 
hot air must be constantly rising. 
I cannot conclude, without insisting with Mr. Jonathan 
Williams on the use of the thermometer at sea ; if commonly 
employed, and the observations made with it recorded, a 
general knowledge might soon be obtained of the average 
temperature of all parts of the ocean, and a fund of curious 
and useful information might be collected, especially respect- 
ing currents and shoals, that to practical navigators could not 
fail of being highly serviceable. 
In another letter, I propose communicating to you the 
