DEEP-SEA EXPLORATION. 
345 
trained crew were able to handle it with alacrity, coiling it nj)on si)ecially prei>ared 
pins as it was hove np or throw it off as rapidly as required for veering. The dredge 
and trawl were hoisted by steam power, a donkey engine being jn-ovided for the 
purpose. It had an ordinary gypsy head, around which several turns were taken 
with the roi»e, which was then attended by hand. The Challenger was the largest 
and best-appointed vessel ever employed in deep-sea exploration, and her subsequent 
achievements, including a successful haul of the beam trawl iu 2,<>o0 fathoms and a 
dredge haul in 3,875 fathoms, are sufficient proof of her efiiciency. 
The introduction of steel-wire dredge rojie on board the United States (loast 
Survey steamer TiUdce in 1877 effected a revolution in deep-sea dredging as complete 
as the use of pianoforte Avire accomplished in the methods of sounding. 
The earlier investigations of the United States Uish Commission were conducted 
on board small vessels loaned by the Navy Department and temporarily eipiipped for 
deep-sea exploration. Hemi) line was used for sounding, also for dredging and 
trawling, an ordinary engine with a single gypsy head being employed for hoisting. 
A marked advance was made in the equipment of the Fi.sh Han'h by the 
introduction of pianoforte wire for sounding and steel-Avire roi»e for dredging. 
All the later imiwovements bearing upon the work of the Albatross Avere embodied 
in her equi])ment, which also inclnded many noA^el ap])liances. 
DREDGING ENGINE. 
I’lates XXVI and xxvii repi’esent the dredging engine, the principal use of which 
is to hoist the trawls and dredges, but it is provided AAuth additional gypsy heads 
for hoisting boats, etc. It Avas built by Copeland & Bacon, of Noav York, according 
to their patents. It has three gypsy heads (the large one of steel) mounted on the 
same horizontal shaft, and driven by a double-cylinder half-trunk steam engine 
throngh the interA^ention of toothed gearing and a moditication of Mason’s friction 
clutch. The engines have locomotive valves, which are actuated by Stephenson’s 
links and eccentrics; the cranks are cast-iron disks; each pair of eccentrics is cast in 
one; the cut-off is effected by the lap on the valves. The machine has a friction 
brake to regulate the paying out of the dredge rope, and also a roller guide, with 
treadle motion, to ])ress the rope aside and ])revent the turns from riding. The 
engine is ])laced on the main deck, forward of the foremast; it takes its steam from 
the main boilers, and may be exhausted either into the main condenser or into the 
atmosphere. 
POV/ER OF THE DREDGING ENGINE. 
The wire rope from the dredge passes over the dredging block at the end of the 
dredging boom, then under a sheave in the heel of the boom, then upward and over a 
block suspended from the accumulator, and then to the central (or large) gypsy 
head of the dredging engine. 
The accumulator (plate xxxi), which is a series of rubber “buffers” moving 
freely on their longitudinal axes by the tension on the dredge rope, becomes a good 
dynamometer. By taking a large number of dynamometer readiugs simultaneously 
Avith indicator diagrams from the dredging engines, noting at the same time the actual 
velocity of the rope as it is measured by the register on the boom sheave and also the 
speed of the engines, and by taking the mean of these quantities Ave shall approach 
very closely to the true conditions. 
