II. H1TDKOGRAPHY. 737 



3017. Tube Lead. For sounding in depths not exceeding 

 1,000 fathoms, and procuring specimens of the sea bottom ; date 

 1872 ; model. In use in H.M.S. " Challenger." 



3018. Specimens of Sounding Line. Used in H.M. ships. 

 No. 1. used in " Challenger " ; No. 2. medium. 



These lines are constructed of the best Italian hemp. 



No. 1 line is one inch in circumference ; 100 fathoms (or 600 feet) weighs 

 18 Ibs. 9 oz. When wet this line breaks at a minimum strain of about 14 

 hundredweight. 



No. 2 line is - 8 inches in circumference ; 100 fathoms weighs 12 Ibs. 8 oz., 

 and it bears a strain of about 10 hundredweight when wet. j 



THERMOMETERS AND APPARATUS FOR PROCURING SEA WATER, 

 USED IN DEEP SEA EXPLORATION. 



3019. Six's Thermometer, with protected bulb. Negretti. 

 Designed by Fitz Roy and Glaisher (about 1860) ; used in H.M. 

 ships " Bulldog " and " Porcupine " in North Atlantic. 



3020. Six's Thermometer. Hydrographic Office pattern ; 

 bulb not protected. Casella ; date 1867. Used in H.M. ships 

 " Lightning " and " Porcupine " in North Atlantic. 



This instrument (the full bulb of which was unprotected by an outer glass 

 casing) was found to be affected by pressure, and gave erroneous results at 

 great ocean depths ; and this led to the construction of the protected bulb 

 thermometer (3021). 



3021. Six's Thermometer. Miller pattern ; bulb protected 

 as proposed by Dr. Miller. Casella; date 1869. In use in 

 H.M.S. " Challenger :" generally adopted, after being tested to 

 three tons on the square inch. 



The full bulb is protected by an outer glass casing. The errors of these 

 thermometers are determined under pressure, and are found to be reduced to 

 the limits of about 1 '2 for depths of 2,500 or 3,000 fathoms. 



Two protected bulb thermometers which were broken by pressure at a 

 depth of 3,875 fathoms in the Atlantic Ocean. 



3022. Johnson's Metallic Self-registering Thermo- 

 meter. Invented by Mr. Henry Johnson (about 1858). Not in 

 general use. 



3023. Saxton's Metallic Self-registering Thermometer 



(about 1855). Used on the United States Coast Survey. Not in 

 general use. 



3024. Water Bottle. In ordinary use for bringing up water 

 from ocean depths. [Superseded in H.M.S. " Challenger " by 

 Buchanan's design.] 



40075. 3 A 



