614 SEC. 15. GEOGRAPHY. 



being cast from the ship, the whole is thrown overboard, the inflated bag 

 floating as the line runs through the attached nipper, the bag keeping 

 immediately over the descending lead. 



On the lead reaching the bottom, indicated by the spring of the bag, no 

 more sounding line will pass through the nipper, and the place where it is thus 

 nipped is the vertical depth of water as marked on the line. 



3014. Massey's self-registering Sounding Machine ; date 

 1800. Adapted for moderate depths. In use in H.M. Navy. 



3015. Ericsson's self-registering Sounding Machine ; date 

 1836. For sounding in moderate depths. 



This instrument records the vertical depth irrespective of the amount of 

 sounding line thrown out from the ship. 



The depth is ascertained by the compression of air within a glass tube, the 

 value of the compression, in accordance with depth, being recorded by the 

 quantity of water passing into the tube as the air is compressed, and a scale 

 adapted to it. 



3016. Cup Lead. For sounding in depths not exceeding 

 1,000 fathoms, and to procure specimens of the sea bottom (about 

 1858) ; model. Originally used in sounding North Atlantic. 



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 0-8 inches in circumference; 100 fathoms weighs 12 Ibs. 8 oz., 

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



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). 



