218 THREE CRUISES OF THE “ BLAKE.” 
tion of Sir William Thomson’s sounding-machine ; the bottom 
and the surface temperatures, taken with the Miller-Casella 
thermometer, were compared from time to time with a standard. 
We obtained in the Caribbean and in the Gulf of Mexico a uni- 
form bottom temperature of 393° Fahrenheit, below six or seven 
hundred fathoms. The cause of this uniform bottom temper- 
ature is to be found in the depth of the passage between the 
Windward Islands, through which the cold waters of the Atlan- 
tic, from similar depths, force their way slowly northward, first 
into the Caribbean Sea, and then into the Gulf of Mexico, 
through the Straits of Yucatan. (Fig. 142.) 
To Commander Bartlett I am indebted for information re- 
specting the lines run between the islands. His report remains 
unpublished in the archives of the Coast Survey. The follow- 
ing extract from one of his letters will show the extent of the 
work done by the “ Blake : " — 
“І connected the islands by running traverses across the ridges. 
From St. Vincent to St. Lucia the ridge was only from 150 to 170 
fathoms below the surface, with a channel of 400 fathoms near St. Vin- 
cent. The channel between’ St. Lucia and Martinique had 500 -fath- 
oms in mid-channel, sloping upward to each island. The channel 
between Martinique and Dominica was a tough one, and I thought I 
should never find a ridge. The soundings increased regularly on a 
ridge to 300 fathoms in mid-channel, where I got a sounding of 883 
fathoms, and then 1,000 fathoms ; beyond this the ridge was some ten 
miles to the westward, with an average depth of 400 fathoms, but I 
found two peaks with only 40 fathoms. The deep water from the Ca- 
ribbean Sea makes in between Guadeloupe and Montserrat, but I 
found a ridge ,of about 300 fathoms connecting Antigua with Guade- 
loupe. ‘In this channel I also found a peak with only 40 fathoms. I 
finished up the line connecting Saba Bank with St. Croix. I found the 
connection perfect, but the ridge has 700 fathoms water on it near St. 
Croix. There is 1,000 fathoms three miles north, and 1,800 fathoms 
five miles south of the ridge. I ran a line from Dog Island to White 
House Shoal, and, back to Sombrero. Here I found a channel about ten 
miles wide, with 1,100 fathoms. The temperature was 38° at 1,100; 
outside, 874° at 1,600, and 365° at 2,500. I shall run a number of 
lines from St. Thomas to Sombrero, to be sure that this channel con- 
nects with the deep water off St. Thomas. I ran a line of soundings 
from the south end of Dominica to Avis Island. The soundings were 
regular at 1,000 fathoms to within ten miles of Avis Island.” 
