Page:Popular Science Monthly Volume 3.djvu/149

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the Fraunhofer lines of the solar spectrum, and the bright lines of terrestrial elements. A glance at Fig. 19 will show at once the result of this investigation. The brightest line (1) of the nebula coincides exactly with the brightest line (N) of the spectrum of nitrogen, which is a double line. The faintest of the nebular lines (3) also coincides with the bluish-green hydrogen Hue Hß, or, which is the same thing, with the Fraunhofer line F in the solar spectrum. The middle line (2) of the nebula was not found to coincide with any of the bright lines of the thirty terrestrial elements with which it has been compared; it lies not far from the barium line Ba, but is not coincident with it.




IT is natural that we should regard with an intense curiosity all the faculties with which our bodily frame is gifted, and that we should desire to preserve them as perfectly as possible. The following remarks are designed to do something toward gratifying that curiosity with regard to one of the most important of our powers, and to give a few hints in respect to things that are hurtful to it.

Our popular physiologies teach us that there is a tube leading from the drum of the ear into the throat, called, from its discoverer Eustachius, the "Eustachian tube." The use of this tube is twofold. First, it supplies the drum with air, and keeps the membrane exactly balanced, and free to move, with equal air-pressure on each side; and, secondly, it carries off any fluid which may be in the drum, and prevents it from being choked by its own moisture. It is not always open, however, but is opened during the act of swallowing, by a little muscle which is attached to it just as it reaches the throat. Most persons can distinctly feel that this is the case, by gently closing the nose and swallowing; when a distinct sensation is felt in the ears. This sensation is due to a little air being drawn out of the ears through the open tube during swallowing; and it lasts for a few minutes, unless the air is again restored by swallowing with the nose unclosed, which allows for the moment a free communication between the ear and the throat. We thus see a reason for the tube being closed. If it were always open, all the sounds produced in the throat would pass directly into the drum of the ear, and totally confuse us. We should hear every breath, and live in a constant bewilderment of internal sounds. At the same time the closure, being but a light contact of the walls of the tube, easily allows a slight escape of air from the drum, and thus not only facilitates and regulates the oscillations of the air before the