The picture in “From the Archive” (“Self-experimenter didn’t suffer,” SN: 1/28/12, p. 32) shows heavy water ice sinking in a glass of water while alongside, light water ice floats. What is not clear is what kind of water is in the glasses. If heavy water ice were in a glass of heavy water, would it also float? Robert Chester, Tumwater, Wash.

The picture shows a heavy water ice cube sinking in normal water. Like normal water, heavy water expands when it freezes, becoming less dense. An ice cube made of heavy water will thus float in heavy water. Christoph Salzmann of University College London offers an illustrative experiment: Fill a glass halfway with heavy water and halfway with normal water. Then drop in a heavy water ice cube. The cube will sink until it reaches the dividing line between the normal and heavy waters, at which point it will float midglass. — Elizabeth Quill

Studies of light are ancient The survey of advances in reflective light and camera innovations (“The digital camera revolution,” SN: 1/28/12, p. 22) recalls the 1964 book Byzantine Aesthetics by Gervase Mathew. The subject matter of religious symbols was important, but so was the technique of setting the colorful tiles. It might be good to take another look at Byzantine art and the Neoplatonism of Plotinus (who died about A.D. 270) and the bridge between Plato’s shadows and the coming theories of light, especially sunlight. Cynthia Shepard, Foster City, Calif.

Aura experiences vary
I have never experienced a migraine
headache (“Head agony,” SN: 1/28/12,
p. 26) but regularly experience auras
like those in the story. The auras come
with stress and are quite beautiful, look-
ing much like the opening scene from
the old television show Bonanza where
the flame starts at one point and then
spreads outward on the map. No doubt
in times past, people may have thought
they were being visited by an angel or
having a supernatural experience.
Joe Kostka, Natrona Heights, Pa.

Memory falters under pressure The inability to recall what happened during a feat that requires great concentration doesn’t apply only to athletes (“Brainy ballplayers,” SN: 1/14/12, p. 22). As a U.S. Foreign Service officer in the 1980s, I served as notetaker during high-pressure, high-level meetings between the United States and Soviet Union. Right after meetings, anxious colleagues would ask what happened. “I don’t know,” I would reply. “I’ll have to read my notes.” My thanks to Science News for explaining why that happened. Bruce G. Burton, Fairfax Station, Va.

Send communications to: Editor, Science News, 1719 N Street, NW, Washington, D.C. 20036 or editors@sciencenews.org. Letters subject to editing.

Available now for the iPad in the iTunes App store.

Science News Prime

Marketplace

Visit sciencenewsprime.org for more information.

A new way to get the latest reports from the frontiers of science, brought to you weekly from the staff of Science News and featuring:

s news articles and briefs
s an in-depth feature article
s rotating columns including
Reconstructions, Earth
in Action, Culture Beaker
and Science News editor
in chief Tom Siegfried’s
new column, Randomness
s shorts on weird creatures,
science newsmakers and
new books

MAGAZINE OF THE SOCIETY FOR SCIENCE & THE PUBLIC
Save time, save
money and give
the magazine that
covers science
in a biweekly,
user-friendly
format. www.sciencenews.org/gift