Mr. Seymour having thus described the form of the instrument, and stated that its construction was solely directed with a view of making it oscillate freely on any plain surface, thrust the block in the fire, and when sufficiently heated, placed it on its angular surface, upon a flat piece of lead. It immediately began to vibrate, producing at first, a kind of singing noise, not unlike that of the simmering of a teakettle, but the vibrations became more and more rapid until a distinct musical sound was produced, which from time to time varied in its pitch, and gave rise to an effect scarcely inferior to that of the Eolian harp. “How extremely beautiful!” said Miss Villers. “And how admirably does it illustrate the theory of musical sounds,” observed Mr. Seymour. “We have here, you perceive, a series of impulses communicated to our ears by the air, at first in slow succession, and by degrees more and more rapidly; at first we hear a rattling noise, then a low murmur, and then a hum, which by degrees acquires the character of a musical note, rising higher and higher in acuteness. It is evident, therefore, from this experiment alone, by showing the correspondence which exists between the pitch of the note and the rapidity of the succession of the vibrations, that our sensation of the different pitches of musical notes originates in the different rapidities with which their impulses are communicated to our ears.” “Pray explain to us the manner in which the block of metal is thus made to vibrate,” said Miss Villers. “It depends,” replied Mr. Seymour, “upon the alternate contraction of the two opposite edges of the metal from the loss of heat; one of the edges coming in contact with the cold lead contracts, and by destroying the balance of the block, causes its opposite edge to come into contact with the lead, and to undergo the same change; and it is by this alternate action that a rapid vibration is produced, occasioning, as you will now readily understand, the musical sounds you have just heard.” The lecture having been concluded, Mrs. Seymour proposed that the party should, at once, proceed to the valley, but the vicar suggested the propriety of first explaining to the children the principle upon which the echo depended.