34 THE LAST CRUISE OF THE CARNEGIE 



found in them, thorium and radium, they hope to get some idea 

 of the age of the Earth. Scientists studying the origin of oil- 

 deposits will be furnished samples. The American Telephone 

 and Telegraph Company wishes to determine the corrosive ef- 

 fects on their cables. Then too, it is now known that bottom- 

 living creatures feed on organic matter found in muds. 



In this same box is kept the brass bucket for collecting diatoms 

 from the harbors we visit. These exquisite microscopic plants, 

 displaying inexhaustible patterns of form, are present in all the 

 waters of the Earth from pole to pole. They are almost the sole 

 food for the larval stages of fish, and are therefore of immense 

 importance. Some of the largest marine creatures use these tiny 

 plants as food. So minute are they that a hundred of them 

 might be placed side by side on the head of a common pin. The 

 harvest of fish has been noticeably increased by adding silicates 

 and phosphates to the water to augment the supply of diatoms, 

 just as nitrates and phosphates are used in agriculture. The 

 work on board was planned to include a study of the relation of 

 these chemicals to the abundance of diatoms and plankton. In 

 fact, the source of the silica in the surface-layers of the ocean, 

 where the diatoms thrive, is not well known, for the great red- 

 clay silica deposits are sometimes several miles below and seem 

 to be increasing in extent. 



In higher latitudes the diatoms show great changes in abundance 

 with change of season, for they are plants and depend directly 

 on sunlight as their source of energy. It is for this reason that 

 they are found in a living state only in the uppermost few hundred 

 meters of the sea, and on the bottom of shallow shore- waters. 

 It is not always realized that sunlight is totally absorbed in the 

 clearest sea-water in less than a mile from the surface. 



Leaving the gear-box we walk aft to the Stevenson meteoro- 

 logical shelter, which gets its name from its designer, the father 

 of Robert Louis Stevenson. Here are housed some of the various 

 instruments used in studying the circulation of the atmosphere, 

 just as the oceanographic equipment is used to give us a picture 

 of currents in the ocean. There are three forms of apparatus 

 for measuring the changes of humidity. One is a motor-venti- 



