Another in the “live and learn” series: I ran across the phase sola topee today and vaguely thought “Shouldn’t that be solar topee?” After all, it’s a pith helmet worn for protection from the sun. But when I looked it up, I discovered that it is in fact sola, a word for an Indian plant, Aeschynomene aspera, whose pith is used for such helmets and whose Hindi name is śolā.
Here’s an enthusiastic description of the hat from Thomas W. Knox in “The English in India” (Harper’s, 1879, p. 570):
The rarest of these things is the sola topee, or ventilating hat — an excellent device to protect the head from the effect of the tropical sun. It is worn almost exclusively by Europeans, is made of pith, covered with white cloth, and is so contrived that the air may freely circulate around the cranium of the wearer. Many of these hats have found their way to America, and it would be well if they should come into fashion for summer use. With the sola topee a sun-stroke is next to impossible — at least so say the sojourners in the East.