ATMOSPHERIC ELECTRICITY.

About a year ago experiments were begun at the request of U. S. Signal Service by Prof. Trowbridge on the subject of atmospheric electricity with a view to learn its value for meteorological purposes. The method employed was that known as the Thompson one and required very delicate instruments. The result is that a beam of light from a gas flame is reflected from a mirror upon a prepared sheet of sensitried paper and the record of any change in the place of an electric needle is thus obtained by photography. The apparatus in use has several new points in its arrangements that will undoubtedly be of great value for future work. A continuous photographic registration of changes in the electricity of the atmosphere has never previously been attempted in this country, and has only twice ever been attempted elsewhere; once at Kew, under Sir William Thompson and Balfour Stewart, and a year ago or so, at Paris, by Mascart, director of the bureau..

The improvements made by Prof. Trowbridge make the Harvard apparatus superior to either of these. As a specimen of the value of these electormetrical records to the ordinary reader, it is stated by Professor Trowbridge's assistant that a change in the direction of the wind is often indicated several hours, frequently four or five in advance, by a change in the electric potential of the air. Rainy weather and coming storms are also foretold by the changes, but the observations are not yet full enough to lead to any decided statements. Observations are also being made with a view to determining what influence altitude has to do on the electric charge of the air, and instruments have already been placed on the top of the new physical laboratory. It is a work of great delicacy, and some time must necessarily elapse before the great mass of results can be worked up. It seems, though, to be the coming thing for indicating the changes in the weather. It has already given good evidence of its ability to foretell changes, not only in the direction of the wind and of the humidity of the air, but also of the other more involved factors which must be taken into account in forecasting the weather. The idea of using it in connection with weather forecasts is entirely original in this country.