254 HAND-BOOK OF ACOUSTICS.
105. Explain how a Tuning Fork can be kept in a state of continued vibration by an electro-magnet.
106. Describe the apparatus, which is used for the purpose of keeping a number of forks in continued vibration, by means of electro-magnets and a single current. What relation must exist between the vibration numbers of these forks ?
107. How may the relative intensities of the sounds of the forks in the above, be modified ?
108. Describe the apparatus used by Helmholtz, in his experiments on the synthesis of Compound Tones.
109. What is a pendular vibration ? Describe a method of obtaining a graphic representation of one.
110. Show by a diagram how to compound two simple associated waves.
111. Given the quality of a musical tone : is it possible to determine the corresponding wave form ? If not, why not ?