34 



WORK OF THE CARNEGIE AND SUGGESTIONS FOR FUTURE SCIENTIFIC CRUISES 



was similar to that used on Beebe's expedition. On calm 

 days it may be lowered for the use of the biologist, who 

 is thus able to dip up floating objects beyond the wash of 

 the vessel. 



A step over the high doorsill and we are in the 

 chemical laboratory. Here each water sample is ana- 

 lyzed for salinity, phosphates, silicates, oxygen, and 

 hydrogen ions. AH these substances are intimately re- 

 lated to the life of plankton. We limit ourselves to 

 such determinations as can be made on board, for we 

 have no room to stow away samples for study ashore. 



There are several unusual features about our 

 chemical work. The salt content of the sea water is 

 measured electrically by a resistance-bridge designed 

 for our use by Dr. Wenner of the Bureau of Standards in 

 Washington. By measuring the electrical resistance of 

 a sample of sea water, we are able to calculate its sa- 

 linity. This method is checked regularly by the con- 

 ventional titration of samples with silver-nitrate solu- 

 tions. 



The apparatus for measuring the so-called "hydro- 

 gen-ion concentration" of sea water at various depths 

 is ingenious. It avoids the use of permanent color 

 standards in test tubes, and gives more accurate read- 

 ings than are ordinarily obtained at sea. It is a modifi- 

 cation of the double-wedge comparator described in 

 technical journals by Barnett and Barnett. 



To analyze for phosphates and silicates, chemicals 

 are added to the specimen to bring about the develop- 

 ment of a certain color, the intensity of which is a meas- 

 ure of the phosphate or silicate present. After treating 

 with the same chemicals a second solution (whose com- 

 position is known) we have only to match the intensity of 

 one color against the other to obtain a value for the un- 

 known sample. The presence of as little as one part of 

 phosphate per billion parts of water can be detected in 

 this way. 



When the reports of the oceanographer, the chemist, 

 and the biologist are correlated, we have a good picture 

 of the life of plankton. We can see what limits of tem- 

 perature and salinity they tolerate; v/hat substances they 

 need for food; and what influence variations in sunlight, 

 oxygen, and acidity have on their growth. 



The usual equipment of a chemical laboratory is 

 more familiar and will be passed by. But there are, be- 

 sides this, microscopes, dissecting instruments, and 

 preservatives for the use of the biologist. 



Over in the corner of the room is a self-recording 

 sea-water thermograph. This device keeps a continuous 

 record of the changes in surface temperature as we sail 

 down the latitudes. A large bulb of mercury is mounted 

 on the outside of the vessel's hull. It communicates with 

 the recorder through a capillary tube. Any changes in 

 the volume of the mercury in the system, due to changes 

 in sea temperature, are transmitted through a hollow 

 coil spring to a recording pen. 



A short walk forward, a few steps up, and we are on 

 the "bridge." From here we can look upward at the 

 lofty rigging, more bewildering in detail than many of 

 our instruments. Or, we may look toward the forecastle- 

 head and see, coiled on the deck, the two great hawsers 

 which serve us for anchor chains. But a weird object, 

 suggesting an automaton in a brass helmet, stands at the 

 center of the bridge, challenging attention. This is the 

 "marine collimating compass." It gives the magnetic 

 declination, or "compass variation" as sailors call it. 



The principles on which it operates are simple 



enough. We wish to find the angular difference between 

 true geographic north and the magnetic north as indicat- 

 ed by the compass. We can use the sun as our point of 

 reference, since we know its true bearing from the ship 

 by using the Nautical Almanac. In the collimating com- 

 pass, the card ordinarily viewed from above is replaced 

 by a set of vertical scales which may be seen by looking 

 horizontally through openings in the sides of the compass 

 bowl. An observer brings the image of the rising sun, 

 let us say, to one of these vertical scales with an ordin- 

 ary sextant and measures the horizontal angle between 

 them. With the sun's image on the vertical scale he can 

 make continuous readings of its position, as the compass 

 swings back and forth with the roll of the ship. By taking 

 the mean of many such readings, he has made an accu- 

 rate measurement from which the declination may be 

 computed. 



This instrument was designed by Peters and Flem- 

 ing of the Department of Terrestrial Magnetism, and 

 was made in its shop. The method is superior to older 

 methods used at sea which depended on hasty readings 

 taken as the sun's image, or a shadow, flits across a 

 moving compass card on a rolling ship. Three observ- 

 ers are required to take a declination measurement. 

 One man's duty has been described. A second reads the 

 altitude of the sun from time to time, for it seldom hap- 

 pens that weather conditions are perfect exactly at sun- 

 rise or sunset, and corrections for altitude must be ap- 

 plied. The third observer is the recorder. He must be 

 a sleight of hand artist, because he has to write down 

 the readings of the other two and keep a second -to -sec- 

 ond record of the time when each of these is made. 



On the starboard wing of the bridge is located an 

 apparatus for collecting the radioactive materials in the 

 atmosphere, which are present in only infinitesimal 

 amounts. When a measured volume of air is drawn 

 through the collector over negatively charged metal foil, 

 the desired particles are deposited on the foil because 

 they carry a positive charge. Let us now follow the ob- 

 server into the atmospheric-electric laboratory, where 

 he will measure the amount of radioactive material col- 

 lected. This electric laboratory is located just abaft the 

 bridge, directly amidships. It is entered from the foot of 

 the steps leading to the bridge. The observer places the 

 metal foil in an ionization chamber where the rate at 

 which the radioactive material produces electrified par- 

 ticles or ions is measured. This rate gives a measure 

 of the amount of radioactive material collected. 



Another instrument counts the ions normally pres- 

 ent in the atmosphere, by extracting them from a meas- 

 ured volume of air. Over the oceans there are usually 

 about 30,000 of these per cubic inch, half with positive 

 charge and half with negative. Under the action of the 

 earth's electric field, positive ions are traveling toward 

 the earth and negative ions upward into the air, giving 

 rise to an air-earth electric current which makes no 

 impression on our senses. The rate at which this inter- 

 change takes place would neutralize the earth's negative 

 charge in a very short time, were there no recharging 

 agent. Up to the present, however, the mechanism which 

 generates the recharging current has not been established, 

 and remains a major problem in studies of the electricity 

 of the earth and atmosphere. 



Penetrating radiation, or "cosmic rays," long have 

 been known to ionize the air. These exceedingly powerful 

 rays can penetrate several feet of lead, and seem to orig- 

 inate entirely outside our solar system. An apparatus 



