Q4 TEMPERATURE OF THE SEA. 
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 oc- 
cupied themselves in preparing the plants which 
they had collected, and in making sundry observa- 
tions. Crossing to Ferrol they made some inter- 
esting experiments 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 na- 
vigators ; for, although the use of the thermometer 
ought not to supersede that of the lead, variations of 
temperature 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 
continue their experiments. It was produced by a 
storm at sea, and obliged the English vessels to re- 
tire from the coast,—a circumstance which induced 
our travellers speedily to embark their instruments 
and baggage, although they were prevented from 
sailing by a high westerly wind that continued for 
several days. 
