This action goes on as long as the person wishes it, and a ringing succession of blows on the bell is the result.

Such a bell, besides being suitable for ordinary service, is an efficient alarm against burglars, provided the door or window by which the burglar enters is made to press the button on the act of opening. It can also be used for telling the height of water in a boiler or other domestic event; and it is used out of doors to indicate the level of water in rivers or reservoirs, and thus forewarn floods. When it is used to announce an outbreak of fire on the premises, the circuit is completed sometimes through the melting of tallow or a very fusible metal alloy under the heat generated by the fire. A better plan is to use a small thermostat," or composite spring s, Fig. 83 of two

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different metals, say brass and iron, soldered back to back, and placed so that when the spring, by curving under the unequal expansion of the two metals, due to the rise of temperature occasioned by the fire, will come into contact with a metal pin P, and thus com

plete the circuit of the battery. Such is the plan of Mr. Edward Bright, C.E., who has also devised the ingenious system of street fire-alarms now introduced into many of the London districts. In this system there are a number of street posts, each containing a handle, by which the person giving the alarm can ring an electric-bell at the nearest fire brigade station, and at the same time enable the officer on duty there to verify the locality and number of the street-post on which the alarm has been given.

OTHER USES.

A very good electric clock has also been devised by M. Hipp, of Geneva, and an elegant pattern of it was exhibited at the recent Paris Electrical Exhibition under the name of "butterfly clock." In this form the pendulum bob was made of soft iron and swung over the poles of an electro-magnet placed beneath it. When the pendulum "slowed" to a certain degree, it made an electric contact by means of a projecting arm, carrying a butterfly shaped vane of mica, and a momentary current of electricity traversed the electromagnet, and gave the pendulum a hitch forward. In this way the rate of the time piece was kept practically constant.

The electric light has been employed with great success in photography, especially in London, where dark and foggy days are so common during the winter months. It has also been applied recently with good results to the photo-chemical process of copying plans

and drawings by exposing transparent tracings of them to a strong light which decomposes a chemical salt in the sheet of paper intended to receive the copy except where the black lines of the design absorb the light.

As a means of foretelling the weather, the telegraph has of course proved exceedingly valuable; and very likely the American storm warnings would be far oftener correct if we had a cable to the Azores, and could ascertain if and when the coming cyclone passed that way. Quite recently there was a proposal before the French Government to lay a cable between the British Island of Mauritius and the French possession. of Reunion in the Indian Ocean, so as to enable Mauritius to forewarn Reunion of approaching cyclones. Indeed, there is a future prospect of an international weather telegraph, connecting all the leading meteorological stations in the world, and exchanging facts and observations with each other. To this end M. Van Ryssellberghe and others have devised their telemeteorographs for automatically observing the state of the weather and telegraphing it to distant places at regular intervals, say, of ten minutes. These beautiful and ingenious instruments attracted much attention at the Great Electrical Exhibition of 1881. Perhaps, when the universal system is in operation we shall have to take the warnings of our own Weather Office in earnest.

The number of experimental apparatus in which electricity has played a part is legion. There is no applied science into which it does not enter, and every art may profit by its aid. The most delicate chronographs for measuring intervals of time are electrical, and register the motions of a very rapidly vibrating

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tuning-fork on barrels of smoked glass. These are very useful instruments in physiological experiments, such as the determination of the speed of thought. The movements of the pulse are also recorded by means of electricity with the sphygmograph, and Dr. B. W. Richardson has applied the microphone to render the beating distinctly audible. It is a somewhat significant fact that, according to the doctor, the human pulse seems to go on saying, "Bother it!"

As a curative agent electricity is becoming more and more useful, and established on a sound scientific basis. Its possibilities in this direction are infinite, not only in the cure of nervous disorders, but in the reduction of tumours by electrolysis, in the dissipation of pain, the enticement of sleep, and the destruction of bacteria. The field is almost virgin-and none can tell what further service the electric current will yet render to the arts of Medicine and Surgery. The searching quality of its power is greatly in its favour; and when properly tempered the application may be painless. At present the cure of physical disease, the noblest of all the manifold uses of electricity, is that which is in the most backward and obscure condition.

Bullet finding by induction balance, Electric lighting, 137