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THE AMERICAN NATURALIST [Vol. XLVII 



and the application of new methods made possible by improved 

 apparatus has led to the dicsovery of certain general laws. 



For example, Professor Gran, using a steam centrifuge capable 

 of centrifuging 1,200 c.c. of sea water at a speed of 700-800 

 revolutions per minute, discovered the unsuspected fact that the 

 smallest pelagic plants, the nannoplankton which pass readily 

 through the meshes of an ordinary silk net, are far more abun- 

 dant than are the larger forms. He found, also, that pelagic 

 plant life is most abundant at depths of 10-20 meters, but be- 

 comes extremely scanty below 100 meters, and he confirms the 

 conclusion of Nathansohn that marine plant-life thrives best 

 where ascending currents bring upward a supply of nitrogenous 

 compounds derived from the decomposition of organic matter in 

 the deep sea. Gran concludes that in the tropics the phyto- 

 plankton consists of numerous species, most of which are rare, 

 whereas in the colder waters there are few species but great ag- 

 .. a fcions of individuals. 



Professor Helland-Hansen made use of a new form of photo- 

 graphic-plate photometer which he himself had invented. He 

 was thus enabled to demonstrate that a good deal of sunlight 

 penetrates to a depth of 1,000 meters, but at 1,700 meters his 

 plates were unaffected by an exposure of 2 hours' duration. The 

 sun's rays at a depth of 500 meters in clear tropical water still 

 retain a definite direction, not having yet become diffuse. But 

 the most important discovery is the fact that the red rays are 

 absorbed more quickly than the blue. Thus little or no red light 

 can penetrate into the depths and the dark red color so char- 

 acteristic of the animals of the deep sea is explained by the fact 

 that, there being no red light where they live, they appear black 

 and are thus rendered invisible. 



The ship was well supplied with oceanographic apparatus, 

 having a number of Ekman's current meters, Kichter's revers- 

 ing thermometers, Petterson-Nansen 's water bottle and Petter- 

 son's insulating deep-sea bottle, enabling one to bring samples 

 of water to the deck and there determine the temperature which 

 the water had when at the bottom of the sea. 



The Michel Sars is certainly to be congratulated upon the 

 success attending their skillful use of this apparatus. For ex- 

 ample, the vessel ventured to anchor in a depth of 400 meters 

 over a hard bottom in the straits of Gibraltar and then to make 

 use of two Ekman current meters, one at a constant depth of 10 

 meters and the other at various depths down to the bottom. 

 They achieved the first accurate quantitative determinations of 



