Náttúrufræðingurinn - 1956, Blaðsíða 31

STORMMÁFUR, NVR VARl’FUGL Á ÍSLANI)!
93
In June 1955 the author discoveretl Common Gulls breeding on a low
grassy islet near Reykjavík, SW-Iceland. The islet, named Korpúll'sstadahólmi,
is close to the shore and is easily accessible on foot during low tide. In the
[jrcsent paper detailed information is supplied about observations made by
several observers on the Common Gulls in thc above locality in 1955. Apart
from the Common Gulls, the following birds were found breeding on tlie
islet: Anas platyrhynchas (3 pairs), Somateria mollissima (c. 50 pairs), Larus
riclibundus (40—50 pairs) and Sterna paradisaea (10—15 pairs).
Ott June 19 a downy young was found on this islet. It was collected and
presented to the Museum of Natural History, Reykjavík. It is almost certain
that this is a Common Gull’s chick. On June 26 a Common Gull’s nest
containing one egg was found on the islet and on June 28 three eggs had been
laid. On July 10 only one egg remained in the nest, another egg — now in
the Reykjavík Museum — was found broken near the nest. The third egg
could not be traced. On July 23 the nest was found to be empty and one
young may possibly have hatched. The downy young and the eggs need not
necessarily have belonged to the same parents, as 4 adult Common Gulls
were seen around the islel in the last week of June.
Trausti Einarsson:
Fast kolefni kemur fyrir í náttúrunni í tvenns konar krystölluðu
formi, annað hvort sem demant eða sem grafít, og er það venjulega
formið. Ennfremur er sót úr kolefni gert, en í kolum er kolefnið
aldrei hreint, heldur er það þá í rnjög flóknum samböndum við
vatnsefni og súrefni. Demant hefur, sem kunnugt er, ýmsa merki-
lega eiginleika. Hann er harðastur allra efna, hefur hörkuna 10, og
getur sorfið hvaða efni sem er. Hann er því notaður við borun og
svörfun og ennfremur sem öxullegur í úrum o. fl.
í öðru lagi brýtur demantur ljós mest allra efna. Ljósbrotstala
lofts er 1, vatns 1,33, glers 1,5—1,7, en demants rúmlega 2,4. Það
er þetta sterka ljósbrot, sem er orsök þeirra eiginleika, er gera