This must be the effect that discos get with their strobe lights.
I've often wondered what you'd see with an optical stroboscope if you
were to go to a hilly site at night overlooking a city. The whole
city is likely to be running from one power grid, which means that
there is three-phase 60 Hz power city-wide, all time-coherent.
I'd assume the total flicker frequency is 360 Hz, because of the
enclosed-arc street lights and luminous-tube ("neon") signs. (Two
blinks per cycle, and time displacements of a third of a cycle should
give you 360 Hz.)
If you set the strobe to about 121 hz, the lights would flicker
according to which of the three phases they were connected to. (A
given light is single-phase).
In high school, we had a very nice cylindrical optical strobe; its
spin axis was crosswise, so you sighted through a diameter (or nearly
so). IIrc, the sighting port was wedge-shaped, with the wider part
toward the scene you were observing. Visibility to the right and left
was maybe 90 degrees, although vertically maybe only 10 deg. or
possibly less. The narrow slit of the wedge, being closer to your
eyes, gave an open time of only a very few percent.
Its rotor had low friction, so coast-down time was quite decent. It
was driven by an air turbine, and the air came from a squeeze hand
bulb with valves. Balance was truly fine. It was all black, and had
no speed indication at all.
Been posting all day; all in one big gulp of snacks, but I probably
won't be posting here much again soon, if at all. Hope I haven't
caused any hardships! Also, hope I haven't done too much to convert
snacks into a banquet. I might start reading my e-mail again soon; no
promises, though. I will get to it eventually, however.
With my best regards,
Nicholas Bodley |@| Waltham, Mass.
Please reply to firstname.lastname@example.org
Opera browser user, registered
Autodidact and polymath to some extent
This archive was generated by hypermail 2.1.3 : Mon Apr 24 2006 - 11:34:48 PDT