Bøjen løfter sig, og bringes ned igjen paa Merke ved at 
man helder rent Vand fra Buretten i Fordunstningsskaalen. 
Det ydre Kar dd hænger i Slingrebøjler. Paa Bun- 
den af Fordunstningsskaalen ligger et Thermometer til 
Maaling af det fordunstende Vands Temperatur. Da det 
ydre Vands Bæreevne forandrer sig med Temperaturen, 
idet Bøjen flyder lettere i koldt end i varmt Vand, træn- 
ger den af Buretten aflæste Vandmængde en Rettelse, for 
at kunne give den virkelig fordunstede Vandmængde, i de 
Tilfælder, at det ydre Vand havde en anden Temperatur 
ved Forsøgets Afslutning end ved dets Begyndelse. 
Thermometer ¢, der hænger ned i det ydre Vand, tjener 
til at aflæse dettes Temperatur ved hvert Forsøgs Begyn- 
delse og Ende. 
Fordunstningsmaaleren stod paa Agterdekket, paa en 
Kappe (nm) lige i Nærheden af Regnmaaleren (2) — (Fig. 2 
Side 2). Denne Plads var vistnok ikke den heldigste, men 
en anden var vanskelig at finde, og den havde den Fordel, 
at Apparatet her kunde staa uforstyrret af andre Gjøre- 
maal. Det havde intet Tag, saaat det optog alt det Regn, 
som faldt derpaa. Naar den faldne Regnmængde var 
større end den fordunstede Vandmængde, vilde Bøjen, idet 
Ringen 7 toges bort, staa med Merket under Vand. Jeg 
tog da med en Pipette en Del Vand ud af Skaalen a, 
indtil Instrumentet kom paa Merke. Denne Vandmængde 
udgjør, regnet efter dens Vægt, Forskjellen mellem Regn- 
mængden og Fordunstningsmengden. Da den første 
disse findes ved Hjelp af Regnmaaleren, kan den sidste 
beregnes. Da den med Pipetten udtagne Vandmængde er 
salt Vand. trænger den paa Pipetten aflæste Mængde en 
Correction, for at udtrykke Forskjellen mellem den Mængde 
ferskt Vand, der er faldt som Regn og den, der er fordunstet. 
Naar Fordunstningen var større end Regnmængden, var 
Fremgangsmaaden den sædvanlige, og Fordunstningsmæng- 
den beregnedes som Summen af det af Buretten heldte 
Vand og den faldne Regnmænede. 
/ 
Paa vor Rejse 1 1876 var Vejret ialmindelighed me- 
get uroligt, og Skibets Rulling og navnlig Sætning bevir- 
kede meget ofte, at Vandet i Fordunstningsskaalen blev 
slængt ud af denne. Derfor fik jeg kun faa Fordunstnings- 
observationer den Sommer. Indhiyningsmaskinen havde, 
naar den var 1 Gang, en lignende Virkning paa Fordunst- 
ningsmaaleren som NSøgangen. I Nolskin opvarmedes det 
ydre Kar dd saameget, at hele Apparatets Temperatur steg 
mange Grader over Luftens og Havvandets. Fra Skor- 
stenen faldt der Sodfiller i Fordunstningskarret. 
For at undgaa disse Ulemper, construerede jeg et nyt 
Apparat, (Fig. 13) der blev brugt i 1877 og i 1878, efter 
samme Princip, men med mindre Dimensioner.  Fordunst- 
H. 
Den norske Nordhavsexpedition, Mohn: Meteorologi, 
Et. 
af 
similar to a part of the sea-surface itself. At the close of 
the experiment, the leaden ring was removed, the buoy 
rose, and was brought down again to the mark on the 
stem by pouring fresh water from the burette into the 
evaporating dish. 
The outer vessel dd was suspended in gimbals. At 
the bottom of the evaporating dish lay a thermometer, for 
measuring the temperature of the evaporating water. As 
the specific gravity of the outer water varies with the 
temperature, and the buoy will float higher in cold water than 
in warm, the quantity of fresh water read off on the 
burette requires a correction in order to determine the true 
quantity of lost by evaporation, provided the 
outer water have a different temperature at the close than 
at the beginning of the experiment. 
water 
A thermometer f. 
partially immersed in the outer water. serves for reading 
off the said temperature at the beginning and end of each 
experiment. 
mounted on the afterdeck, on 
the cap of a hatchway (nm), in immediate proximity to the 
rain-gauge (2) — fig. 2, p. 2. 
The atmometer was 
This was certainly not the 
best of places; but a better could hardly have been found 
where the apparatus was out of harm’s way and caused 
no inconvenience. ‘lhe atmometer had no cover, and ac- 
cordingly received all the rain that fell on its surface. 
When the quantity of fallen rain was greater than that of 
the water evaporated, the buoy would, on the ring r being 
removed, remain depressed below the mark on the stem. 
the latter being under water. I then took with a pipette 
a quantity of water from the dish a, till the instrument 
reached the mark. This quantity of water gives by its 
weight the difference between the quantity of fallen rain 
and of the water evaporated. The former being found from 
observation of the rain-gauge, the latter can be computed. 
The water taken out with the pipette being salt, requires 
a correction, in order to find the difference between the 
fresh water, fallen as rain, and the fresh water evaporated. 
When the amount of evaporation had execeeded the 
quantity of fallen ram, the imstrument was adjusted in 
the usual way, the evaporation being computed as the sum 
of the water poured from the burette and the quantity of 
rain fallen. 
During the cruise in 1876 the weather wasas a rule 
very boisterous, and the rolling, and more particularly the 
pitching, of the vessel, caused the water to be repeatedly 
thrown out of the evaporating dish; hence, only a few 
experiments could be made that summer. The vibration 
caused by the donkey-engine produced an effect on the atmo- 
meter similar to that occasioned by a rough sea. When 
the sun was shining, the outer vessel dd became so heated 
that the temperature of the whole apparatus rose many 
degrees above that of the air and the water of the sea. 
Flakes of soot, too, fell from the funnel on the water 
evaporating. 
With a view to obviate these drawbacks, I constructed 
a new apparatus (Hig. 13), which was used in 1877 and 
1878, on the same principle but of smaller dimensions. 
18 
