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On December 30, 1872, off Vigo, Spain, the Challenger's scientific voyage began in earnest as they conducted the first dredging operation.

Sighted the coast of Spain this morning but are still 150 miles from Lisbon. At 10 o'clock this morning the first cast of the dredge was made & bottom obtained at 1500 fathoms but in hauling up the dredge 100 fathoms of line was lost over board. The dredge was again cast but came up bottom upwards but on another attempt being made they succeeded in bringing up mud and several species of Fish from a bottom of 1125 fathoms, or nearly 1 1/2 miles; on the mud being analysed numerous insects were found in it--the fish are preserved in bottles. The Dredge is of Iron & not unlike a pig trough with a net over it & weighs with the weights attached several hundred weight. The strain on the line is very great as it reaches the bottom & to ease it, several gutta percha ropes are spliced to it which will stretch when strained. The Dredging line is about the thickness of a man's two fingers. When dredging the Ship is hove to, & the Dredge is let down from the main yard & hauled up by a small steam engine & the line coiled away on the upper deck to dry; 1200 fathoms of line will take one hour in reaching the bottom & 3 hours in hauling up.

Two of Challenger's modern power features would best be used during the dredging operations. The steam engine, which assisted the corvette's sails when necessary in moving the ship, were run constantly during dredging to help the ship hold a steady position while the dredge and its thousands of feet of line were lowered and reeled in.

The small donkey engine on the deck was used to haul in the dredge lines, a formidable task had it been necessary to complete it by hand.