258 HAND-BOOK OF ACOUSTICS.
180. Calculate the Differentials produced by a Fourth, Major and Minor Sixth, a Tone, and a Semitone.
181. When the following is played on a Harmonium, what Differential Tones may occur ?
s :— |f :n |r :— |r :— d :— |-n :—|r :d |d :—|t| :— d :—|-
182. Upon what instruments are Differential Tones very prominent ?
183. When is the Differential intermediate in pitch between its two generators ?
184. What is meant by a Differential Tone of the 1st order? Show by an example how Differential Tones of the 2nd and 3rd order are produced.
185. How is the vibration number of a Summation Tone related to the vibration numbers of its generators ?
186. Explain by means of diagrams or otherwise, what is meant by Interference of sound waves.
187. What is meant when it is said that two waves are in the same or opposite phase ?
188. Describe and sketch any apparatus that may be used to demonstrate the fact, that two sounds may be so combined as to produce silence.
189. Describe by help of a diagram the sound waves that emanate from a vibrat'ng fork, clearly showing their alternate phases.
190. If a tuning-fork be revolved before the ear, alternations of intensity are observed ; clearly explain the whole phenomenon and its cause.
191. How may Chladni's plates be used to illustrate the phenomenon of interference ?
192. How are the intensities of sounds related to the amplitudes of their corresponding sound-waves ?
193. What is a beat ? What is the law connecting the vibration numbers of two tones and the number of beats they generate per second ?
194. Carefully explain how a beat is produced.
195. How would you proceed to prove experimentally that the rapidity of the beats increases as the interval between the two generating tones increases ?
196. Explain the principle of the Tonometer.
197. A Tonometer consists of 50 forks, each fork is 4 vibrations per second sharper than the preceding, and the extreme forks form an exact Octave. What is the pitch of the lowest fork ?
198. Two harmonium reeds when sounded together produce 4 beats per second. The pitch of one of them is then slightly lowered, and on again sounding it with the other, two beats per second are heard. It is then further flattened and again two beats per second are heard. Was it originally sharper or flatter than the unaltered one? Answer fully.