  The first N-body simulation of interacting galaxies, even producing spiral
arms, was performed by Erik Holmberg in Lund (1941), not with a numerical
computer, but by his arrangement of movable light-bulbs and photocells to
measure the luminosity at each bulb and thereby estimate the gravitational
force. A decade later, and with the arrival of the first programable computers,
computations of galactic dynamics were performed, which were later transferred
into a N-body simulation movie. I present here the background details for this
work with a description of the important elements to note in the movie which
may be retrieved at http://ttt.astro.su.se/~po .
