58 Questions Jbr Solution relating to Meteorology, 



sooner or later be deduced from the value of thermometrical 

 soundings ! 



Temperature of Shoals. — Jonathan Williams first made us 

 acquainted with the fact, that water is colder on shoals than in 

 the open sea. MM. de Humboldt and John Davy confirmed 

 the discovery of the American observer. Sir Humphry Davy 

 attributed this curious phenomenon, not to submarine currents, 

 which, when arrested in their course, rise along the sides of 

 banks and glide to the surface, but to radiation. By means of 

 radiation, especially when the sky is clear, the superior beds of 

 the ocean ought certainly to be greatly cooled ; but every de- 

 gree of cold, except in the polar regions, where the temperature 

 of the sea is near zero, occasions an increase of density, and a 

 descending movement in the beds cooled. Suppose an ocean 

 without bottom, the beds in question sink to a great distance 

 from the surface, and must slightly modify the temperature; 

 but when the same causes operate on shallow water, the cooled 

 beds accumulate, and their influence must then become very 

 perceptible. 



Whatever may be in this explanation, every one will perceive 

 how much the art of navigation is interested in verifying the fact 

 announced by Jonathan WiUiams, which some recent obser- 

 vations seem to contradict ; how eagerly also meteorologists 

 will receive the comparative measurements of the temperature 

 of superficial waters in the open sea and above sand-banks ; and, 

 in particular, how desirable it is to determine by means of the 

 thermometograph, the temperature of the bed of water which 

 rests immediately on the surface of the shoals themselves. 



Height of Waves. — The young officers of the Bonite will 

 probably be greatly surprised if we assure them that none of 

 their predecessors have fully answered the following questions : 

 What is the greatest height of waves during tempests ? What 

 are their greatest transverse dimensions? What is the rate of 

 their progress ? 



Observers have been usually satisfied with forming an esti- 

 mate of the height. But, in order to shew how erroneous such es- 

 timations may be, and the influence which the imagination exer- 



