The Cause of Streaks upon Lath and Plaster Walls

Abstract

IN reply to Mr. Thomas D. Cope's letter in NATURE of January 21, it may be stated that he is correct in supposing that the best explanation of the streaks on the plaster he refers to is that they are due to the hot-air molecules driving the dust particles into contact with the plaster, and the colder the plaster the weaker is the power of the cold-air molecules next it to resist the deposition. This tendency of hot air to deposit its dust on cold surfaces can be seen in a very marked way in any house heated with hot water or steam. Wherever a hot pipe comes through a wall there will always be found a dirty vertical streak on the wall just above the hot pipe, caused by the stream of hot air rising from the pipe depositing its dust on the cold surface.