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has drawn special attention to the frequent occurence of ice
masses in those parts of the sea, which we should expect to
be most free of ice, although he seems not to have appreciated
the real cause of the phenomenon.
Another remarkable phenomenon, which certainly must
be due to the influence of the cold water-stratum below, was
observed on the evening of the 30th August. Nordenskiöld
writes:
»The temperature of the water near the surface varied
between + 1° and + 1°.6 C, the temperature of the air was
found -f 1°.5 to + 1°.8 C. Notwithstanding both air and water
had a temperature higher than 0°, ice began to appear at the
surface of the sea (which was quite calm and unruffled) in
the shape of needles or a thin film of frozen water. Several
times before I had witnessed the formation of ice in the arctic
sea, when the temperature of the air was above zero. In this
case, when the temperature of the upper water-stratum was
also above zero, the formation of the ice clearly must depend
upon a radiation of heat either upwards to the air or
downwards to the cool water-stratum at the bottom.»
I think the most plausible explanation of the phenomenon
is: that the undermost layer of the fresh-water at the surface
of the sea, being cooled below its freezing point [= — 0°.76 C
corresponding to the spec, weight = l.ono], gave up ice, which
on account of its higher spec, volume rose to the surface of
the calm sea and thus made the impression upon the spectators
of a spontaneous formation of ice-crystals from the surface-
Very interesting is the description of the encounter of the Vega with
ice in the midst of the waters of the Lena river in the afternoon of the
28th August. From the map (plate 25) and the section VII the reader will
get an idea of the situation.
tlncontro di nnovo ghiaccio. — Fnmmo anche costretti a farlo dall’
apparire di alcuni pezzi di ghiaccio che per la loro natura indicavanó che
non si erano staccati da molto tempo dal banco principale. Ed in fatti
verso le 2, il ghiaccio cominció a spesseggiare, ed alle 4 pom. divenne tanto
denso, da obbligarci ad avanzare lentamente e con continuo maneggio di
timone.»
tin presenza del ghiaccio nessun sensibile cambiamento avviene nella
temperatura e colore delle acque. — Contrariamente a quanto ci era sin qui
■accaduto, l’approssimarsi del ghiaccio non fu annunciato da alcun sensibile
cambiamento di temperatura e di scoloramento dell’ acqua; la temperatura
dell’ acqua alia superficie ed a qualche metro di profonditá si mantenne al
disopra de’ 3° ed il colore continuo ad essere di un giallo terreo, le quali
cose indicavanó che non eravamo ancora usciti dall’ estuario della Lena» .. .
[Spedizione ártica Svedese, G. Bove.]
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