From J. A. BRISCOE
Judy Turner’s upward pointing icicle (Letters, 2 and 16 November) could
be explained as follows.
Spider-web filaments are virtually invisible because our eyes hardly
ever focus exactly on them.
Such a filament may have been anchored on a stone or something on the
bottom of the birdbath, before it was refilled. Dewdrops would form on the
web and eventually run down where they would freeze if the temperature difference
near the ground was just right.
On the night in question, these conditions must have held for a considerable
time, in order to form an icicle pointing upwards at the angle of the invisible
spider web.
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J. A. Briscoe Harrogate, North Yorkshire
