THE DEPTHS OF THE OCEAN. 201 
repeated. The most ingenious and beautiful contrivances for 
deep-sea soundings were resorted to. By exploding heavy charges 
of powder in the deep sea, when the winds were hushed and all 
was still, the echo or reverberation from the bottom might, it was 
held, be heard, and the depth determined from the rate at which 
sound travels through water. But, though the explosion took place 
many feet below the surface, echo was silent, and no answer was 
received from the bottom. Ericsson and others constructed deep- 
sea leads having a column of air in them, which, by compression, 
would show the aqueous pressure to which they might be subject- 
ed. This was found to answer well for ordinary purposes, but in 
the depths of " blue water," where the pressure would be equal to 
several hundred atmospheres, the trial was more than this instru- 
ment could stand. 
Mr. Baur, an ingenious mechanician of New York, constructed, 
according to a plan which I furnished him, a deep-sea sounding 
apparatus. To the lead was attached, upon the principle of the 
screw propeller, a small piece of clock-work for registering the 
number of revolutions made by the little screw during the descent ; 
and, it having been ascertained by experiment in shoal water that 
the apparatus, in descending, would cause the propeller to make 
one revolution for every fathom of perpendicular descent, hands 
provided with the power of self-registration were attached to a 
dial, and the instrument was complete. It worked beautifully in 
moderate depths, but failed in blue water, from the difficulty of 
^ hauling it up if the line used were small, and from the difficulty of 
getting it down if the line used were large enough to give the re- 
quisite strength for hauling up. 
424. But, notwithstanding these failures, there was encourage- 
ment, for greater difficulties had been overcome in other depart- 
ments of physical research. Astronomers had measured the vol- 
umes and weighed the masses of the most distant planets, and in- 
creased thereby the stock of human knowledge. Was it credita- 
ble to the age that the depths of the sea should remain in the cat- 
egory of an unsolved problem ? It was a sealed volume, abounding 
in knowledge and instruction that might be both useful and profit- 
able to man. The seal which covered it was of rolling waves 
many thousand feet in thickness. Could it not be broken ? Cu- 
riosity had always been great, yet neither the enterprise nor the 
