MUSEUM OF COMPARATIVE ZOOLOGY. 157 



is therefore always pressed between the two chocks by the elastic force 

 of the spring, which may be regulated as desired. To regulate the buf- 

 fer for any definite frictlonal resistance, clamp it to the rope, and move 

 the regulating screw V weil inwards ; then suspend from the buffer a 

 weight equal to the resistance decided upon. Move the regulating screw 

 outwards until the buffer slides down the rope under the influence of 

 the suspended weight. Since the chock R is always screwed " home " 

 in clamping to the rope, the buffer remains regulated for prolonged use 

 with the same resistance ; and, if the latter prove satisfactory, it is 

 probable that the regulating screw need not be touched again for a 

 whole cruise, if the buffer be rinsed in lye-water each time after use. 



A crank or key, W, is fitted to the squared heads of the regulating 

 and adjusting screws, on which it locks with a spring snap, the latter 

 being operated by the bent arm at one end of the crank. The stud at 

 the other end of the crank is for adjusting the screws J J. 



The cast-iron messenger, X, is in two parts, connecting with each other 

 by a dovetail, — or something of similar purpose. 



Professor Agassiz and Commander Bartlett added the funnel-shaped 

 trap, and also the leather cushion, Y, around the valve seat, after a pre- 

 liminary trial with the apparatus. 



'Working the Apparatus. 



It is necessary to first regulate the buffer to cushion the stoppage of 

 the falling weights, which are, cylinder and frame 38 lbs., clamp 4 lbs., 

 messenger 8 lbs., total 50 lbs. The "Blake" adopted a resistance of 

 about 80 lbs. (this resistance being, of course, constant during the whole 

 movement of the buffer), it having been found that a blow of that force 

 resulted in no injury to the apparatus. 



On the ascent the buffer must withstand, not only the weight of the 

 fifty pounds of metal, but also the resistance which the water offers to 

 the passage through it of the several parts of the apparatus. Moreover, 

 when the cylinder emerges from the water, it is full of that liquid, and 

 with this increased weight would overcome the stated resistance of the 

 buffer, and force the latter downwards until the lead was reached. To 

 meet these conditions it was not thought advisable to increase the re- 

 sistance of the buffer, which would involve a heavier blow against the 

 apparatus, but a rope-yarn seizing or stop was placed on the rope about 

 fifteen or twenty feet below the buffer, beyond which the latter could 

 not pass. 



Having secured the buffer to the rope about five or six fathoms above 



