TEMPERATURE OF THE SEA. 21 



and the American colonies. The principal secre- 

 tary of state had recommended them to Don Rafael 

 Clavigo, recently appointed director-general of the 

 maritime posts, who neglected nothing that could 

 render their residence agreeable, and advised them 

 to embark on board the corvette Pizarro bound for 

 Havana and Mexico. Instructions were given for 

 the safe disposal of the instruments, and the captain 

 was ordered to stop at Teneriffe so long as should 

 be found necessary to enable the travellers to visit 

 the port of Orotava and ascend the Peak. 



During the few days of their detention, they occu- 

 pied themselves in preparing the plants which they 

 had collected and in making sundry observations. 

 Crossing to Ferrol they made some interesting ex- 

 periments on the temperature of the sea and the 

 decrease of heat in the successive strata of the 

 water. The thermometer on the bank and near it 

 was from 54 to 55'9, while in deep water it stood 

 at 59 or 59-5, the air being 55. The fact that the 

 proximity of a sand-bank is indicated by a rapid 

 descent of the temperature of the sea at its surface 

 is of great importance for the safety of navigators ; 

 for, although the use of the thermometer ought not 

 to supersede that of the lead, variations of tempera- 

 ture indicative of danger may be perceived by it long 

 before the vessel reaches the shoal. A heavy swell 

 from the north-west rendered it impossible to con- 

 tinue their experiments. It was produced by a storm 

 at sea, and obliged the English vessels to retire from 

 the coast, a circumstance which induced our trav- 

 ellers speedily to embark their instruments and bag- 

 gage, although they were prevented from sailing by 

 a high westerly wind, that continued for several days. 



