IN the last number of NATURE a report is given of the first of Dr. Tyndall's Christmas â Lectures to Juveniles,â on the Motion and Sensation of Sound. In that lecture Dr. Tyndall shows how the reflection of sound can be made manifest to an audience by means of a sensitive flame ; and, according to the closing words of your report, Dr. Tyndall states,â â Never before have these phenomena been made visible. Hitherto these effects have been investigated by the sense of hearing ; I have now been able to prove them by appealing to your eyes.â