40 PASSAGE FROM MADEIRA 
Appendix XVI.) The periods of oscillation were found to be as fol- 
lows : the maxima at nine a. m. and nine p. m., and the minima at 
three a. m. and three p. m. The variation was 1 of an inch, and was 
found to be very regular, from latitude 3° 30' N. to 4° S. 
We had now heavy deposits of dew on several fine and cloudless 
evenings. Indeed the sun had scarcely set before the ship was quite 
wet with it. One of the essential requisites supposed necessary by 
Dr. Wells for a deposit of dew, was certainly wanting in this case, 
viz., that " The temperature of the body on which it is deposited, 
should be considerably lower than the surrounding air." The tem- 
perature of the air and ship having remained the same for several 
days at about 78°; all objects, hammock-cloths, spars, sails, and 
ri ggi n g> so f" ar as could be ascertained, showed the same. And at 
the time when the dew was observed to be most copious, we had a 
fine breeze. It has generally been supposed that dew never falls off 
soundings. This at least is an old saying among seamen, but our 
observations are at variance with this notion, for as far as every 
indication went, both by sounding and blue water, we certainly had 
no bottom. 
The supposed position of the Triton Shoal was now passed over, 
and examined carefully in the same manner as heretofore described, 
sounding at the same time with two and three hundred fathoms 
of line. Nothing of the kind was perceived, nor was there any 
indication of soundings in the discoloration of the water, or any 
change in its temperature. 
We next sailed for a vigia laid down on the chart. 
On the 7th November at noon we were in longitude 18° 20' W., 
and latitude 3° 30' N. Here we first experienced the influence of the 
equatorial current, and found it setting west by north at the rate of 
half a mile per hour. This vigia was not seen. I then stood for 
Bouvet's Sandy Isle, or its reported position. We saw nothing of 
it whatever. I was very desirous of continuing my search farther 
to the west, from the report I had seen of various vessels having 
experienced shocks of earthquakes, and the belief having been en- 
tertained that shoals might have been formed by them. The equa- 
torial currents having been felt, I was aware that in getting farther 
to the west, I should lose the opportunity of examining the locality 
where that distinguished navigator, Admiral Krusenstern, supposed 
he saw a volcano. I therefore gave up proceeding farther to the 
westward in this latitude, and hauled up for its position. 
