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 392° 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 unpublished in the archives of the Coast Survey.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 : " ^ 



" I 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, vnth. 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 Avith 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 

 fmished 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, 37F at 1,600, and 36F 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." 



