In 1910, Halley’s Comet was scheduled to return on its 76-year flight through the heavens. As the world prepared to watch the once-in-a-lifetime event, modern science announced it would be even more spectacular, predicting Earth would actually pass through the comet’s tail. In February, scientists began to make conflicting observations.

From Berkeley, Calif., came “‘If the astronomers are right in their estimation of the amount of cyanogen gas in the tail of Halley’s comet, and if that body’s…