NARRATIVE OF THE CRUISE 



33 



exact time interval between outgoing signal and returning 

 echo. With this information we can easily calculate the 

 depth, for the velocity of sound in sea water is known. 

 It is roughly one mile a second, depending, however, on 

 the temperature and salinity. But as these factors for 

 each water level are determined on board, we are able 

 to sound with an unusual degree of precision. For ex- 

 ample, the observer reports that it took two seconds for 

 the echo to return. This means that the sound wave 

 traveled about two miles, and the sea is one mile deep. 

 This is the underlying principle, although actually the 

 procedure is somewhat more complicated. 



The great advantage of this method is that the ship 

 need not heave to and consume one or two hours for a 

 sounding with line and lead. A sonic depth may be made 

 with the ship on her course in from five to ten minutes. 

 We are able to check these soundings by the old-fashioned 

 lead weight, and do so on alternate days. 



In the large box on the floor are our pressure ther- 

 mometers. With these we have an ingenious method for 

 checking the depths recorded sonically and by wire. Be- 

 sides this, the marvelous instruments can tell us pre- 

 cisely at what distance from the surface each of the 

 "Nansen bottles" was reversed. 



These German-made thermometers are of two types. 

 Some are protected from the enormous pressures en- 

 countered in the deeps, and give the true temperature. 

 Others are unprotected, and give a fictitious reading: 

 the sum of the true temperature and the effect of the 

 pressure exerted mechanically on the naked bulb by the 

 weight of the column of water above it. The difference 

 between the readings of such a pair is then a measure of 

 the pressure. By rather complicated calculations we 

 may then convert this to meters of depth. 



The thermometers are sent down, inverted, in their 

 frames on the side of the Nansen bottles. They are given 

 time to assume the temperature of the surrounding water 

 and are then reversed along with the bottle, when the 

 messenger comes down the wire from the surface. This 

 reversal breaks the thread of mercury in the tiny capil- 

 laries in such a way that the changes in temperature and 

 pressure encountered on the way back to the surface will 

 not be registered, and the observer on deck can get a 

 true picture of conditions at the desired depth. 



By the use of these readings and the salinity values 

 for each sample, we are able to calculate "dynamic 

 pressures" for each water level to the bottom. Plotting 

 the figures on a chart we can determine the speed and 

 direction of the ocean currents below the ship- -a subject 

 of great importance to oceanography. These charts are 

 made in much the same way as weather maps prepared 

 by the Weather Bureau--bascd as they are on pressure 

 readings taken at a multitude of stations, from which 

 winds can be predicted. 



There are more direct means for measuring ocean 

 currents. We may trace the course, speed, and direction 

 of floating objects. This is not satisfactory, for only the 

 surface current is represented, and the effect of chang- 

 ing winds on the object may confuse the true picture. A 

 more useful method is to lower from an anchored ship an 

 instrument similar to an anemometer. We had insuffi- 

 cient power for hauling in a deep-sea anchor, and so we 

 relied entirely on the "dynamic -pressure" computations. 



The configuration of the ocean floor is of great in- 

 terest to seismologists studying the movements of the 

 earth's crust. Oceanographers also are able to explain 

 certain peculiarities of ocean currents by the contour of 



the ocean bed. But snormous areas are still unexplored. 



On the wall of the control room hangs the German 

 multithermograph which was referred to when we looked 

 into the Stevenson meteorological shelter. Below it is 

 an inflation-balance for use in connection with soundings 

 of the upper atmosphere. Rubber balloons filled with 

 hydrogen are released from the deck. These extremely 

 light globes are deflected from their upward course by 

 every breath of air they meet. By following them with a 

 theodolite, an instrument for measuring elevation and 

 direction through vertical and horizontal angles, we can 

 study the air currents at heights up to six or seven 

 miles. Besides the general scientific interest in the 

 movements of the earth's atmosphere, the aviator some 

 day will come to rely on pilot charts based on these 

 soundings, just as the mariner relies on wind and cur- 

 rent charts for the ocean surface. 



Before leaving the control room we must glance at 

 the long array of switches, galvanometers, batteries, 

 and ammeters stretched along a table against the star- 

 board wall. Although it is part of the equipment for 

 measuring the elements of the earth's magnetic field, 

 some of this apparatus contains small pieces of steel, 

 and must be set up well away from the observatory 

 domes. One observer sits at this table to control the 

 constant- speed motor for the "marine earth inductor" 

 which we shall see later. He is in communication 

 through a brass speaking tube with the second observer 

 in the dome. At given signals he records the readings 

 of the ammeters or galvanometers before him. 



In the control room we also find the Sperry gyro- 

 scopic pitch-and-roU recorder. Magnetic measurements 

 at sea usually are affected by small errors caused by 

 rolling, pitching, and scending of the vessel. Though 

 small, these errors are important where accurate de- 

 terminations are desired of progressive changes in the 

 earth's magnetism and of their distribution- -as on the 

 Carnegie . A study based on records from this instru- 

 ment has shown that when the vessel heads on any one of 

 the four cardinal points of the compass, no error is in- 

 troduced into the measurements. A record of the rolling 

 and pitching of the ship during magnetic stations can be 

 studied later at headquarters to detect these disturbing 

 effects. 



We have spent a long time in the cramped quarters 

 of this little room, but one can see that in it lies the cen- 

 tral nervous system of the magnetic and oceanographic 

 equipment. A few steps down and we have left the 

 quarter-deck. Standing in the waist of the ship we see 

 curious nets hanging from the whale-boat platforms. 

 These long cones of silk bolting-cloth are used to collect 

 plankton. They are towed from the ship during oceano- 

 graphic stations, and may be lowered to any depth de- 

 sired. 



It is true that the lack of fishing and dredging equip- 

 ment deprived us of the excitement of bringing up fan- 

 tastically shaped monsters from the deep. But in the 

 plankton nets we can catch a hundred bizarre forms to 

 every one recovered from a dredge; we can find animals 

 painted with all the colors of the rainbow, whereas the 

 deep-sea organisms are either black or red. Anyone 

 who has once seen these exquisite creatures through a 

 microscope will never again envy the man with a deep- 

 sea dredge. 



Two parallel booms supporting a net between them 

 project over the water from the fore rigging- -a glorified 

 pirates' plank, as someone has suggested. This boom 



