The contrivance for turning the thermometer over at the bottom of the sea may be described as a vertical propeller, to which the instrument is pivoted. So long as the instrument is descending the propeller is lifted out of gear and revolves free; but as soon as the ascent commences, the action is reversed, the propeller falls into gear with a pinion connected with the thermometer, and by these means the thermometer is turned over, and after one turn it remains locked and immovable. The engraving, Fig. [318], shows the general arrangement, T being the thermometer, S a metal screw connected with the frame of the thermometer by a wheel-and-pinion movement at W; S† is the stop for arresting the movement of the thermometer when it has made one complete turn.

The atmospheric recording thermometer (Fig. [319]) differs from the deep-sea thermometer by not having the double or protected bulb, as it is not required to resist pressures. In this form of the instrument, the thermometer is turned over by a simple clock movement, which can be set to any hour that may be desired. It is fixed on the clock, and when the hand arrives at the hour determined upon, and to which the clock has been set as an alarum clock is set, a spring is released, and the thermometer turns over as before described. A wet and dry-bulb hygrometer is also arranged on the same plan. For observatories, or where it is important to obtain hourly or half-hourly records of the temperature, twelve or more thermometers are placed on a frame, and these are turned over by clockwork one after the other at every hour or half-hour as required.

The reader can hardly fail to perceive that powerful aid to the investigation of the laws of nature must be afforded by such instruments as we have described. And we have but taken an example here and there of the scientific uses of the recording principle, selecting those that are most readily understood, or that are connected with matters coming home to the business and bosom of every one. The science of meteorology does not deal with subjects which furnish merely amusing speculation for the hour. Forecasts of storms and cyclones would often save many lives and much valuable property; and our dependence upon meteorological conditions cannot be more forcibly illustrated than by reference to the disastrous floods which this year (1875) desolated some districts of France. Meteorology has received a great impulse from the introduction of recording instruments; and the vast number of results which are now hourly recorded must lead to the certain development of the science, and its reduction to exact laws. For even the winds obey laws—laws as definite as those which control the motions of the planets; and could we but take into account the whole of the circumstances upon which the movements and other conditions of the atmosphere depend, we should be able to forecast the weather with the same certainty as—thanks to the great and simple law of gravitation—we predict eclipses or other astronomical phenomena. Already, by aid of the telegraph, it is often possible to send a day’s warning of approaching storms to localities lying in their probable track. The Signal Service, which is a Department of the United States War Office, has a corps of meteorological observers spread over the length and breadth of the States, who send every eight hours, to a Central Office in Washington, a report of the force and direction of the wind, height of the barometer, &c. The officer at Washington sends back by telegraph to the public press a synopsis of each day’s weather, and points out what weather will probably follow; but if any city or port be threatened with a storm, special telegrams are sent. Thus, a warning of the approach of a great storm, which entered the American continent at San Francisco on the 22nd Feb., 1871, was sent to Cheyenne, Omaha, and Chicago, twenty-four hours before the storm reached these cities, which it was foreseen lay in its track. Although the hurricane did much damage at some of these places, it would probably have been far more destructive had not the inhabitants been prepared for its approach.

An elegant form of barograph or recording barometer has been brought out, which is small, but sufficiently accurate for all ordinary purposes. It is founded on the aneroid, which, as everybody knows, is an instrument for indicating atmospheric pressure by the changes of form it produces in a thin circular metallic box, partially exhausted of air. The ordinary form of the aneroid is very sensitive and portable (sometimes it is made only the size of a small watch), and bears an index needle moving over a graduated disc; which arrangement is in the barograph aneroid, replaced by a long lever, carrying an ink tracing point in contact with the face of a cylinder that is caused by clockwork to make one revolution per week. On the cylinder is spread a printed paper diagram, divided by lines for each day of the week and each hour of the day, and on this the tracing point marks a continuous curve, showing all the fluctuations of the barometric pressure. The diagram is removed at the end of the week, and a fresh form adjusted to the cylinder. The impressed papers thus form a permanent and continuous record, from which the height of the barometer, at any given moment, may be read off.

THE PHONOGRAPH.

Everything yet contrived in the way of recording instruments is eclipsed in wonder and interest by one which is among the latest marvels of the age. It is a recording instrument, and more than a recording instrument, for it can reproduce to the senses the very phenomena it records; and these same phenomena are the most familiar in their effects, and, at the same time, so subtle and delicate, that the impressions they convey are not generally thought of otherwise than in connection with our finest intellectual and emotional perceptions. We are alluding to the phonograph, which can register for us music and song, and articulate human speech in all their tones and modulations, and, like an aërial spirit, address them to the ear again, as often as we wish, and thus

Inform the cell of hearing, dark and blind;

Intricate labyrinth, more dread for thought

To enter than oracular cave,

Strict passage through which sighs are brought,