nasal and highly comic, whilst the sopranos would emulate railway whistles and screech fearfully; and supposing the specific gravity of the air was continually and materially changing, our voices would never be the same, but alter day by day, according to the state of the air, so that the "familiar voice" would be an impossibility. A bell rung in a gas jar containing air emits a very different sound from that which is produced in one full of hydrogen--a simple experiment is easily performed by passing a jar containing hydrogen over a self-acting bell, such as is used for telegraphic purposes. (Fig. 113.) [Illustration: Fig. 113. A. Stand and bell. B B. Tin cylinder full of hydrogen, which may be raised or depressed at pleasure, by lifting it with the knob at the top, when the curious changes in the sound of the bell are audible.] _Sixth Experiment._ Some of the small pipes from an organ may be made to emit the most curious sounds by passing heavy and light gases through them; in these experiments bags containing the gases should be employed, which may drive air, oxygen, carbonic acid, or hydrogen, through the organ pipes at precisely the same pressure. [Page 111] _Seventh Experiment._ One of those toys called "The Squeaking Toy" affords another and ridiculous example of the effect of hydrogen on sound, when it is used in a jar containing this gas. (Fig. 114.) [Illustration: Fig. 114. The squeaking toy, used in a jar of hydrogen.] _Eighth Experiment._ An accordion played in a large receptacle containing hydrogen gas demonstrates still more clearly what would be the effect of an orchestra shut up in a room containing a mixture of a considerable portion of hydrogen with air, as the former, like nitrogen, is not a poison, and only kills in the absence of oxygen gas. _Ninth Experiment._ Some very amusing experiments with balloons have been devised by Mr. Darby, the eminent firework manufacturer, by which they are made to carry signals of three kinds, and thus the motive or ascending power may be utilized to a certain extent.