72 



være uforholdsmæssig store, en Anskuelse, som ved de 

 senere Undersøgelser fuldstændig er bleven modbevist. Rig- 

 tignok er det paa den engelske ChaLLengerexpedition iagt- 

 taget. at de i den hede Zone fra Havbunden optagne Vand- 

 prøver ved at henstaa nogen Tid vise Overmætningsphæno- 

 mener. men dette vil jo ikke være vanskeligt at forklare. 

 naar man erindrer, at Våndet i de store Dyb selv i Æqva- 

 toregnene er meget nær iskoldt. Det følger nemlig af sig 

 selv. at de til en saa lav Temperatur svarende Luftmæng- 

 der ikke kunne boldes oploste. naar Vandprøverne ved læn- 

 gere Tids Henstand antager de tropiske Egnes bøie Luft- 

 temperatur. Stærkest taler de paa den norske Expedition 

 iidførte Luftbestemmelser for. at Tryktilvæxten med Dyb- 

 den ikke kau have nogen Indfly deise paa Mængden af den 

 i Sovaudet opløste Luft. Tager man nemlig Middelet af 

 Dybder, Temperaturer og Kvælstofmængder for alle de fra 

 Puncter under Overfladen stammende Vandprøver, hvori 

 der paa denne Expedition er foretaget Luftbestemmelser, 

 erholder man til et Middeldyb 693 Favne (1267 Meter) en 

 Middeltemperatur — 0." 05 og en midlere Kvælstofgehalt 

 13.99 CC. per Litre, det vil sige, Våndet i Dybet indehol- 

 der gjehnemsnitlig næsten 0.5 CC. Kvælstof mindre, end 

 det ved sin Temperatur vikle kunne bolde opløst under en 

 Atmosphæres Tryk. 



Naar man erindrer, at Trykket i Havdybene ikke 

 dreier sig om Atmosphærer men om Hundreder af Atmo- 

 sphærer, saa rna åtte man dog vente, at dets Indflydelse 

 (om det havde nogen) vikle give sig tilkjende ved Urégel- 

 mæssigheder af paaviselig Størrelse, og man er, da dette 

 ikke i mindste Maade er Tilfældet, berettiget til den Slut- 

 ning, at Trykket ikke besidder nogen Evue til i mærkbar 

 Grad at ophobe Luftmængderne i de store Dyb. Paa den 

 anden Side maa det fornuftigvis antages, at Våndet i de 

 dybere liggende Lag ikke kan afgive noget af sin Luft. da 

 det jo paa Grund af det der herskende Tryk vil kunne 

 holde oplost overveiende større Mængder end de. der nogen- 

 sinde ere forefundue. 



Den rimeligste Slutning af de senere Tiders Obser- 

 vationer over disse Gjenstande vil saaledes være den. at en 

 Vandprøve, saalænge den beånder sig under Overfladen, 

 uforandret vil beholde den samme Luftmængde eller rig- 

 tigereKvælstofmængde 1 , som den havde absorberet, da den 

 sidste Gang befandt sig i Overfladen udsat for Luftens frie 

 Indvirkning. 



Nu er den Luftmængde, som Sovaudet absorberer af 

 Atmosphæren, bxn edsagelig afhængig af Våndets Temperatur, 

 idet Barometerstandens Variationer ligeoverfor større Tem- 

 peraturdifferentser kun har en underordnet Betydning. Heraf 

 følger, at de Vandmasser, der have absorberet sin Luft- 

 mængde under varmere Eimmelstrøg, . maa være forholdsvis 



1 Den absorberede Surstofmængde er ftemttg i aogen Grad af- 

 hængig af Dyrelive( og andre Tilfældigheder, saaledes al de( tierligi 



""in i den tidligere All Iling vil være del Rigtigste ai anvende 



Kvælstofmængden s Maa] for den samlede Lufl ugde. 



vailing there. has been wholly refuted by the results of 

 later observations. True. the samples of water obtained 

 at great depths within the tropics on the 'Challenger' 

 Expedition were found to exhibit the phenomena of super- 

 saturation when allowed to stand over some time : this. 

 however, is easily explained. if we call to mind that the 

 water at great depths. even in equatorial regions, has a 

 temperature hut little above zero. Hence it naturally fol- 

 lows, that the quantity of air correspionding to so lo w a 

 temperature cannot be retained on the samples of water 

 having stood over sufficiently long to acquire the high tem- 

 perature of the atmosphere in tropical climates. The air- 

 determinations performed on the Norwegian Expedition 

 afford the strangest proof of the fact. that the increase of 

 pressure with the depth does not exert any appreciable 

 influence on the proportiou of air in sea-water. Now. if 

 we compute the mean depth. temperature, and amount of 

 nitrogen for all the samples of water from below the sur- 

 face examined for air-determinations, the result will .be as 

 follows: mean depth 693 fathoms (1267 metres); mean 

 temperature — 0.°05; mean amount of nitrogen 13.9'.' " 

 per litre. which shows that in the depths of the ocean the 

 proportiou of nitrogen averages 0.5 w less than could be 

 absorbed by sea-water of the temperature pre vailing there 

 with the pressure of one atmosphere. 



If we call to mind that the pressure in the depths 

 of the sea is not computed even by tens. but by hundreds 

 of atmospheres. its influence, if any. must surely. one wouhl 

 imagine, occasion irregularities of appreciable magnitude: and 

 we may therefore safety conclude, since no such disturbance 

 can be detected, that pressure does not perceptibly increase 

 the amount of air at great depths. On the other hand. there 

 is every reason to infer, that the water in the lower strata, 

 owing to the immense pressure. cannot part with any of 

 its air. the quantity actually absorbed never being even 

 approximately so great as such a pressure would enable it 

 to retain. 



From the latest observations throwing light on this 

 question, we may therefore reasonably infer. that all sea- 

 water below the surface retains undiminished the quantity 

 of air. or rather of nitrogen. 1 which it absorbed when last 

 at the surface. in direct contact with the atmosphere. 



Now. the quantity of air absorbed by sea-water is 

 niainlv dependent on the temperature of the latter, the 

 rise or fall of the barometer, as compared with consider- 

 able differences in temperature. being in this case of but 

 little moment. Hence it follows. that the proportion of air 

 absorbed by sea-water in warm climates is small compared 



1 Tlir amounl "f oxygen absorbed bj sea-water depending to :i 



certain exterit <>n the presenc )' animal life and other aocidental 



oauses, the amount of nitrogen may, with greater precision, lic as- 

 sumed i" n'iu'.'si>iit the total amount of air — n standard ul' measure- 

 ini'111 adopted in the preceeding Memoir. 



