262 



THE POPULAR SCIENCE MONTHLY. 



Fig. 4. 



mental principle being the detachment of a weight when the bottom is 

 struck. The weight is a 64-pound shot (E, Fig. 1), cast with a hole 

 through it. An iron rod (A B) passes through this hole, with an open- 

 ing or chamber at the lower end " armed " with tallow. When the in- 

 strument strikes, the end of the rod is driven into the material of the 

 bottom, which fills the chamber. At the same time a pair of hinged 

 arms (D) at the top, which were upright in the descent, fall down and 

 release the cord (C), which sustains the ball by a leather collar below. 

 As the loops of the sling are relieved from the teeth of the arms, the 

 rod slips through the hole in the shot, and comes up alone with its en- 

 closed sample of sediment. The difficulty with this machine was the 

 washing out of the material in the ascent. This was remedied by 

 Commander Dayman, by adapting a valve, opening inward, to the ter- 

 minal chamber of the rod. 



In 1860 the assistant engineer of H. M. S. Bull-dog contrived a 

 dredging-lead that combined the principle of Ross's clamm with the 

 disengaging weight of Brooke. It is an ingenious and well-known 

 machine, though hardly as simple as could be desired. Prof. Thom- 

 son thus describes it : 



" A pair of scoops (A) close upon one 

 another scissors-wise on a hinge, and have 

 two pairs of appendages (B), which stand 

 to the opening and closing of the scoops in 

 the relation of scissor-handles. This ap- 

 paratus is permanently attached to the 

 sounding-line by the rope (F), which in the 

 figure is represented as hanging loose, and 

 which is fixed to the spindle on which the 

 cups turn. Attached to the same spindle 

 is the rope (D), which ends above an iron 

 ring. E represents a pair of tumbler-hooks, 

 fastened likewise to the end of the sound- 

 ing-line ; C a heavy leaden or iron weight, 

 with a hole through it wide enough to al- 

 low the rope (D) with its loop and ring to 

 pass freely ; and B a strong India-rubber 

 band, which passes round the handles of 

 the scoop3. In the figure the instrument 

 is represented as it is sent down and before 

 it reaches the bottom. The weight (C) 

 and the scoops (A) are now suspended by 

 the rope (D), whose ring is caught by the tumbler-hooks (E). The 

 elastic ring (B) is in a state of tension, ready to draw together the 

 scoop-handles and close the scoops, but it is antagonized by the weight 

 (Cj, which, pressing down into a space between the handles, keeps 

 them asunder. The moment the scoops are driven into the ground by 



Otho Friedkioh Mclw.b's Dkedgk, 

 a. d. 1750. 



