NARRATIVE OF THE CRUISE 



35 



carried on board measures the amount of this energy 

 received by the earth. Over the oceans this accounts 

 for most of the ionization of the atmosphere. 



Intimately connected with the number of ions in the 

 air is its electrical conductivity, or its ability to carry 

 an electric current. It is measured in this laboratory 

 with an automatic photographic recorder. A stream of 

 air is drawn through a duct past a cylinder at its center. 

 The ions in the air cause a current of one millionth of a 

 millionth of an ampere to pass through the air between 

 the duct and cylinder, and a delicate electrometer meas- 

 ures this current as the air's conductivity. 



The air over the sea is much more free of dust than 

 over land, but the influence of this pollution on the ele- 

 ments of atmospheric electricity is so great that sys- 

 tematic "dust counts" must be made even far from land. 

 Some years ago, when the volcano Krakotoa erupted, 

 such quantities of dust were blown into the atmosphere 

 that it took two years for it to settle over the earth. 

 Even in normal years pollution may vary from 1,000,000 

 particles per cubic inch to a few thousand. When dust is 

 abundant, the atmospheric conductivity is decreased and 

 the potential gradient rises to as much as 300 volts per 

 meter. The Aitken counter is used to determine the pol- 

 lution of the atmosphere. When moist air is suddenly 

 expanded, the water present condenses as droplets, pro- 

 vided some dust particles are present to act as centers 

 of condensation. In the Aitken counter, the droplets so 

 formed are enumerated and not the dust particles them- 

 selves. Other materials besides dust act as centers in 

 the counter, for it is believed that such particles as salt 

 spicules, and even aggregates of water or ammonia mol- 

 ecules, may act as condensation centers. 



In the chart room under the bridge is the navigation- 

 al equipment including sextants (sixteen of them), ba- 

 rometers, log books, marine charts, and pilot books. 

 There are six desks where the observers do their com- 

 puting. Complete sets of graphs, tables, and calculating 

 books are at hand to facilitate the work. These desks 

 are always filled except when a magnetic or oceano- 

 graphic station is being occupied; for a large part of our 

 duties consist in preparation of records. Large win- 

 dows supply plenty of air and light to the men at work. 



In the center of the chart room stands the "standard 

 compass," which furnishes a correct reading for mag- 

 netic north. The "earth inductor" in the forward dome, 

 and the "deflector" in the after observatory, both use 

 this compass for standard magnetic readings. 



Visitors have often expressed surprise that such a 

 well-equipped vessel had no gyroscopic compass, or 

 "metal mike," as it is referred to by sailors. The ap- 

 paratus may be employed to actuate an auxiliary device, 

 which is fast becoming standard equipment on ocean 

 liners, and steers the ship automatically on any desired 

 heading. But on a sailing ship the course must be con- 

 stantly changed to take advantage of wind and squalls. 

 The gyroscope would have required precious power for 

 operation, and would have introduced magnetic materials 

 on board. For these reasons it was out of the question. 

 Besides this, we were seldom trying to make a beeline 

 from one port to another. 



We shall now climb into the forward observatory 

 dome to inspect the marine earth inductor. It deter- 

 mines the "dip" of the magnetic needle, or inclination. 

 It is essentially a rotating coil of wire which is connect- 

 ed to current or potential meters in the control room. 

 Any coil rotating in a magnetic field, with its axis 



perpendicular to the lines of force, will generate a cur- 

 rent in the circuit in which it is placed. It is on this 

 principle that ordinary dynamos operate, except that they 

 use either permanent magnets or electromagnets, where- 

 as we use the feeble magnetic field of the earth. 



If we move the coil around to such a position that its 

 rotation axis is parallel to the lines of force (pointing 

 exactly to the magnetic pole), no current will be gener- 

 ated. This is true because the magnetic field is being 

 cut so that the effect of one half of the coil exactly neu- 

 tralizes the effect of the other. So when the observer in 

 the control room signals that no current is being pro- 

 duced, the man in the dome reads off the angle of incli- 

 nation. In actual practice the procedure is somewhat 

 more complicated than this. 



In the after dome is the "deflector" which gives us 

 the strength of the magnetic field acting on the compass 

 needle. Briefly, we balance the effect on the compass of 

 a small magnet of known strength against the effect of 

 the earth's magnetism. In other words, we find how far 

 a measured artificial magnetic field deflects the compass 

 from its normal position. 



Modern magnetic charts of all oceans are based 

 largely on the work of the Carnegie . So promptly are 

 our observations computed and forwarded to the world's 

 hydrographers, that the "Variation Chart for 1930," 

 published in October 1929, by the United States Navy, in- 

 cluded our measurements through September. These 

 charts are used, of course, by air pilots as well as by 

 mariners. 



The cabin on the Carnegie occupies the space ordi- 

 narily used for cargo on a sailing ship. It can be entered 

 by companionways from the quarter-deck or from the 

 chart room. Although there are no portholes, because 

 the room is below the water line, good ventilation and 

 light are afforded by several large skylights. Everything 

 possible was done to make our living quarters comfort- 

 able. Each observer has his own stateroom, a wise pro- 

 vision, because the working hours for some of the men 

 are very irregular. Each one may decorate his room in 

 his own way, and can secure a semblance of privacy. 



In the cabin is the ship's library. There are books 

 of reference, technical handbooks, general literature 

 and an extraordinary collection of books of polar explor- 

 ation and oceanography. In addition, each man has ample 

 space in his stateroom for his personal choice of read- 

 ing. 



There is a splendid phonograph with a good assort- 

 ment of records, bought chiefly by the observers them- 

 selves. A card table near the library occasionally is 

 swept clear of typewriters and account books for a game 

 of bridge or poker. Photograph albums and a highly 

 prized guest book lie in a corner of the bookshelf. This 

 register contains many famous names from every cor- 

 ner of the earth, and was one of the two books rescued 

 from the flames in Samoa. 



The center of the room is taken up by our dining 

 table. Around this are eight ordinary cane-bottomed 

 bentwood chairs, with brass screws instead of iron ones. 

 They are not fixed to the floor as in most vessels. This 

 little detail does much to disguise the fact that we are 

 cooped up in a ship. Anyone who has travelled in an 

 ordinary steamer will know how uncomfortable the usual 

 swivel chair can be--made as it is to accomodate the 

 fattest passenger. Only on the very rough days is it 

 necessary to brace ourselves at the table. 



But even the cabin cannot be kept free of scientific 



