350 SCIENTIFIC RECORD FOR 1882. 



pour from the Gulf. The stream varies from 50 to 100 miles in width, aud 

 its velocity and temperature are both greater in the middle tha,u on the 

 edges. The maximum rate of the current observed is said to be five 

 miles per hour, and its average rate is perhaps two and a half. 



Instead of running in a trough, as some observers have described it, 

 the stream from the Bahama Banks to Hatteras passes over a rather 

 even plateau, growing narrower to the northward. The mistake of sup- 

 posing a trough or groove to exist has evidently been made by the cur- 

 rent carrying away the bight of the sounding-line, and thus a greater 

 deiJth being shown. This error is common to all soundings made with 

 rope in a current. The bottom in the path of the stream, at 400 fath- 

 oms, seems to be swept clean down to the hard coral rock. The cold 

 bands described by previous observers do not seem to have been met 

 with, and appear to have been due to local rain-squalls or other causes 

 producing accidental inequalities of temperature. Before the limits and 

 velocity of the Labrador or inshore cold current can be described accu- 

 rately, further soundings and serial temperatures are necessary. 



A deep-sea thermometer devised by Dr. Siemens was used on board 

 the Blake, and was found principally useful in verifying the tempera- 

 tures, which can be ascertained with much more ease and rapidity by 

 the Miller-Casella thermometer. 



The action of the Siemens tliermometer depends upon the variations 

 in the electrical resistance of metals caused by changes of temperature. 

 Two resistance coils, one of which is so arranged as to be lowered into 

 the sea to any required depth, are connected with a Wheatstone's bridge 

 and a Thomson's mirror galvanometer. The galvanometer being ad- 

 justed to show zero when the resistances experienced by the coils are 

 equal, the resistance of the coil on board ship is made equal to that of 

 the one lowered overboard by applications of ice or warm water, and its 

 temperature, which will be that of the submerged coil, ascertained by an 

 ordinary thermometer. In all trials the accuracy and trustworthiness 

 of the Miller-Casella deep-sea thermometer were demonstrated. As 

 opportunities offer this examination of the Gulf Stream is being con- 

 tinued. 



Under the direction of the British Admiralty, hydrographic surveys 

 have been prosecuted on the shores of Great Britain, in the Eed Sea 

 and Indian Ocean, and on the coasts of Borneo, China, Corea, Japan, 

 Australia, the Fiji Islands, West Indies, and Newfoundland, employing 

 five sloops of war, six smaller vessels, seventy-nine officers and nearly 

 six hundred men. 



The officers of the Indian marine survey have continued the survey 

 of the long Indian coast line and the publication of excellent charts. 



French surveyors have been engaged in perfecting detailed surveys 

 of the French coasts and the northern coasts of Africa and correcting 

 the charts of the Grecian Archipelago, while pushing forward the sur- 

 veys of the coasts and rivers of Cochin China and the Gulf of Tonquin. 



