Professor Cross's Lecture.

Professor Charles R. Cross of the Institute of Technology, lectured last evening in the Jefferson Physical Laboratory on the acoustic principles underlying the art of telephony.

He said that sound has three and only three elements or characteristics; namely, intensity, which is dependent on the amplitude of the vibration of the sounding body; pitch, depending on the rate of vibration, and timbre or quality due to the form of vibration. When these three elements are determined the sound is determined. Therefore we should be able to reproduce any given sound. This may be done by means of the electrical current, and when it is accomplished in this way we have the telephone.

The lecture was illustrated by numerous experiments, all of which were very successful and helped to make the more intricate parts of the subject clear. The lecture was well received.