612 SEC. 15. GEOGRAPHY. 



3001. Optical Opposite. Raper. An instrument for deter- 

 mining and preserving a position in a direct line between two 

 objects. 



3002. Beam Compasses, tubular. 



3003. Beam Compasses, bar, metal, 



SOUNDING MACHINES AND APPARATUS USED BY ELM. SHIPS IN 

 DEEP SEA EXPLORATION. 



3004. Clam, for bringing specimens of the sea bottom. Sir 

 John Ross; date 1818. Designed and used by Sir John Ross in 

 H.M.S. "Isabella" in Baffin Bay. 



The claw is kept open by hinged arms within ; whilst thus open the outer 

 case is kept up, and a spike connected with the arms projects below the 

 claw. On striking bottom the spike forces the arms up ; this releases the 

 outer case ; as the claw closes the case slides down, and the contents in claw 

 are secured. 



3005. Brooke's Hod, for bringing up specimens of the sea 

 bottom, and weight detaching apparatus (about 1856). By Mr. 

 Brooke, Midshipman, United States Navy. Used, with various 

 modifications, to 1868. 



In the first instrument employed in the United States Navy the valve 

 securing the specimen of the sea bottom was not applied, quills being inserted 

 in the tube for that purpose. The hook, with the wire and ring, supports the 

 sinker weight as long as there is strain on the sounding line ; the moment 

 that^strain ceases by the rod touching sea bottom, the sinker weights turn 

 the suspending hook, and the wire being released the sinkers slide off as the 

 rod is drawn upwards. 



3006. Brooke's Hod, another mode of detaching sinker 

 weights ; date 1857. Used in sounding North Atlantic. 



3007. Skead's Weight Detaching Apparatus ; date 1357. 



By Mr. F. Skead, Master R.N., H.M.S. " Tartarus." Used in 

 Mediterranean Sea survey. 



A 68-lb. shot (represented by the wooden ball, exact size) is slung with 

 wire, and the detaching apparatus attached. On reaching sea bottom, the 

 small weight on the apparatus, which had till this time been kept above the 

 hook by the weight of the shot, is freed, and, falling, reverses the hook ; 

 the shot is thus left behind. The small weight is roughed to secure a small 

 portion of the sea bottom. 



3008. Bonnici's Weight Detaching Clam ; date 1857. 

 By Mr. C. Bonnici. Used in Mediterranean Sea survey. 



A 68 Ib. shot (represented by the wooden ball) is slung with wire, and the 

 claw attached, the weight of the shot preventing the claw opening. On 

 reaching sea bottom and the line slackened, the arms of the claw fall by their 

 own weight, and the sinker is released. 



