Atmosphere, and on the Density of Sea -water. 31 



unsettled weather, as a couple of instances will be sufficient to 

 prove. 



March 17th. N. lat. 4^ W. long. IS^ 80". 



The showers in each instance were accompanied l»y hard gusts 

 of wind, and thunder and lightning. The rain-water, the tem- 

 perature of which was ascertained, was collected in a glass as it 

 ran from the awning. 



The equatorial regions appear to be particularly subject to 

 storms, violent rain, and electrical phaenoniena, the effect of 

 which, in diminishing the temperature, seems to afford a na- 

 tural explanation of the comparative coolness, both of the atmo- 

 sphere and the ocean, that we experienced each time we passed 

 the line. 



The temperature of the sea, it has been asserted by some 

 writers, is subject to little or no diurnal variation. That this 

 remark is far from correct, is evident from the slightest inspec- 

 tion of the Meteorological Journal : it is an opinion that could 

 be formed only from hypothetical views, ill-founded. The fact, 

 as the .Journal exhibits, is, that the diurnal change of the tem- 

 perature of the sea is very nearly as great as that of the incum- 

 bent atmosphere. From all tlie observations 1 could make, 

 when the circumstances were most favourable to accurate results, 

 when the weather was fine, the sea smooth, and the land at a 

 great distance, it appeared to me, that the maximum tempera- 

 ture is about three in the afternoon, and its minimum towards 

 .sunrise. I shall give a single example in detail. 



April 



