SEPT. 1768 TENERIFFE 13 
be imagined by its height, which Dr. Heberden of Madeira, 
who has been himself upon it, gave as 15,396 feet! The 
Doctor also says that though there is no eruption of visible 
fire from it, yet that heat issues from the chinks near the top 
so strongly, that a person who puts his hand into these is 
scalded. From him we received, among many other favours, 
some salt which he supposes to be true natron or nitrum of 
the ancients, and some exceedingly pure native sulphur, 
both which he collected himself on the top of the mountain, 
where large quantities, especially of the salt, are found on 
the surface of the earth. 
25th. Wind continued to blow much as it has done, so 
we were sure we were well in the trade. Now for the first 
time we saw flying-fish, whose beauty, especially when seen 
from the cabin window, is beyond imagination, their sides 
shining like burnished silver. Seen from the deck they do 
not appear to such advantage, as their backs, which are dark- 
coloured, are then presented to view. 
27th. About one this morning a flying-fish, the first that 
had been taken, was brought into the cabin; it flew aboard, 
chased, I suppose, by some other fish, or may be because he 
did not see the ship; at breakfast another was brought, 
which had flown into Mr. Green the astronomer’s cabin. 
28th. Three birds were to-day about the ship: a swallow, 
to all appearance the same as our European one, and two 
Motacille ; about nightfall one of the latter was taken. 
About eleven a shoal of porpoises came about the ship, and 
the fizgig was soon thrown into one of them, but would not 
hold. 
29th. Employed in drawing and describing the bird 
taken yesterday; called it Motacilla avida. While the 
drawing was in hand, it became very familiar, so much so 
that we had a brace made for it in hopes of keeping it alive ; 
as flies were in amazing abundance on board the ship, we 
had no fear but that the bird would have a plentiful supply 
of provision. 
About noon a young shark was seen from the cabin 
1 12,300 feet by more recent measurement. 
