October 17, 1913] 



SCIENCE 



547 



dissolved oxygen and acquired a supply only 

 by diffusion from the atmosphere. 



If ocean waters were aerated solely by diffu- 

 sion from the atmosphere we should expect the 

 upper strata to possess a larger amount of dis- 

 solved oxygen than the lower. But such is not 

 the case in the tropical Atlantic, for instance. 

 Here the smallest amounts, one to two cubic 

 centimeters per liter of water, are found be- 

 tween the depths of 150 and 800 meters, while 

 the water between 1,100 and 1,500 meters con- 

 tains twice as much or more, that is, three to 

 four cubic centimeters per liter.* 



The Black Sea affords an excellent illustra- 

 tion of the inefficiency of diffusion in the proc- 

 ess of aeration. Owing to the greater salinity, 

 hence greater density, of the lower water the 

 vertical currents do not penetrate to the bot- 

 tom of the sea; that is, the lower portion is 

 permanently stagnant and oxygen can pass 

 into it only by diffusion. But Lebedinzeff^ 

 found no dissolved oxygen below a depth of 

 200 meters, the aerated portion comprising only 

 about eight per cent, of the maximum depth of 

 this body of water. 



Similar conditions are found in many fresh- 

 water lakes during the summer period of 

 thermal stratification. At this time the cool 

 lower stratum of water is cut off from contact 

 with the air by the warm upper stratum and 

 can receive new supplies of oxygen only by 

 diffusion from the latter. If the former loses 

 any or all of its dissolved oxygen during the 

 stagnation period, however, the deficiency con- 

 tinues until the autumnal overturning takes 



In view of these facts it is evident that some 

 agent other than diffusion is responsible for 

 the aeration of bodies of water. In lakes aera- 

 tion is accomplished by the vernal and au- 

 tumnal overturning of the water and its subse- 

 quent circulation for a longer or shorter period. 

 In speaking of the aeration of ocean waters 



4 Schott, "Physische Meereskunde, " p. 72. 



5 ' ' Aus der Fischzuchtanstalt Nikolsk, ' ' No. 9, 

 p. 113. 



« Birge and Juday, Bull. XXII., "Wis. Geol. and 

 ISTat. Hist. Survey. 



7 "The Depths of the Ocean," p. 253. 



Helland-Hansen' states that " these gases are 

 absorbed at the surface from the atmosphere 

 and are carried by currents even into the 

 deepest parts of the ocean in varying amounts." 

 C. Juday 



AN ANOMALOUS EFFECT OF RONTGEN RAYS 



An unexpected effect due to X-rays has 

 been brought to my attention, which I be- 

 lieve has been hitherto unobserved. The re- 

 sult is obtained as follows: 



Let a sensitive plate be placed film down 

 upon a silver coin, and let a second silver 

 coin be so placed above the plate that areas of 

 contact of the plate and coins partially over- 

 lap. Now let the plate and coins which are 

 enclosed in a light-tight box be exposed to 

 X-rays from above. 



When the plate is developed, the result is of 

 course a light area with but little effect due 

 to radiation transmitted by the upper coin 

 and a dark area due to the secondary radia- 

 tion from the coin below. The anomaly ap- 

 pears at the area of overlapping coins. Since 

 this receives its impression both from trans- 

 mitted rays and from the secondary rays 

 from the coin below, it is to be expected that 

 this area will be darker than the remaining 

 area shaded by the upper coin. The opposite 

 is true, and the area of the overlapping coins 

 is always lighter, as though the secondary 

 radiation from the lower coin cancelled the 

 effect of the rays transmitted hy the upper 

 coin. When small plates of lead are substi- 

 tuted for the silver coins, the effect is re- 

 versed, and the area in question is darker in- 

 stead of lighter. This is the result that one 

 would expect. 



The writer has tried many combinations of 

 metals in this manner and has found that the 

 anomalous effect occurs in a number of cases, 

 as for two gold coins, copper coins, gold and 

 silver, and many others. 



The question which the case suggests is in 

 regard to the manner in which the neutraliza- 

 tion of the effect of the transmitted rays is 

 brought about by the secondary rays and why 

 it seems to be so complete in some cases and 

 not in others. The writer has tried to ascer- 



