Glazebrook, "Light," p. 157.

Galileo was severely censured and imprisoned for daring to maintain that the earth moved round the sun, and revolved on its axis.

For a full account of Animated Pictures the reader might advantageously consult "The Romance of Modern Invention," pp. 166 foll.

Tyndall, "On Sound," p. 75.

A Broadwood "grand" is made up of 10,700 separate pieces, and in its manufacture forty separate trades are concerned.

Twelve notes higher up the scale.

It is obvious that in Fig. 136, 2, a pulse will pass from A to B and back in one-third the time required for it to pass from A to B and back in Fig. 136, 1.

The science of hearing; from the Greek verb, ἀκούειν, "to hear."

"Organs and Tuning," p. 245.

The Edison Bell phonograph is here referred to.