144 Normat 58:3, 144 (2010)
Summary in English
Frank Nielsen, Rømers Tandhjul.
(Danish).
The Danish scientist Rømer, known
for his determination of the velocity
of light, was a correspondent of New-
ton, Leibniz and Huygens. He made an
invention of cogwheels, allowing both
wheels to rotate at constant angular
velocities as they engaged with each ot-
hers teeth. It was based on epi- and hy-
pocycles, i.e. curves traced by a fixed
point on a circle rolling inside or outside
a given circle. Unfortunately the details
were lost, but a reconstruction has la-
ter been found in the collected works of
Huygens. Taking this as a point of de-
parture, the article explains the mathe-
matics behind the construction, based
on beautiful geometric properties of the
curves involved.
Frank Bengtsson, Om Christoffer
Dybvad, hans Euklid kommentar og un-
dertrykt strid om cirkelkvadratur (Da-
nish)
This is a historical survey of the Danish
adventurer Christoffer Dybvad (1577/8-
1622) who ended up imprisoned for li-
fe and ordered by the King to comp-
lete some mathematical treatises. Be-
fore that he had written the first Da-
nish commentary on Euclid, and been
one of the critics along with Pell of the
squaring of the circle proposed by Long-
omontanus (see Sørensen, Kragh Nor-
mat 55:3 (2007)). A detailed discussion
of the length of inscribed polygons given
by successive halving of angles is inclu-
ded as basis for the discussion on the
defective argument of Longomontanus.
Hugues Verdure, Density of Rational
Points on an Algebraic Curve(English).
The article is inspired by Mazurs theo-
rem that on a plane curve which has an
infinite number of rational points those
are dense in a component of the curve.
This fact is shown for the case of the
line, the quadric and more interestingly
the cubic.
Ulf Persson, Martin Gardner 1914-
2010 (Swedish).
This is an obituary of Martin Gardner
from the viewpoint of my teen-age en-
counters with his works up to a conclu-
ding epistolary interchange at the very
end of his life.
Ulf Persson, Benoit Mandelbrot 1924-
2010 (Swedish).
This is an obituary of Benoit Mandel-
brot explaining the unconventional na-
ture of his career and talents as well
as his role in naming and promoting
fractals.
Ulf Persson, Kochs snöflinga
(Swedish).
This is a short presentation of the snow-
flake curve first presented by Helge von
Koch in 1904. In particular an explicit
parametrization is given and some ques-
tions are asked.
