of being advanced in the same way; and when it is borne in mind that the force of waves, the ebb and flow of tides in rivers, the influence of training works in estuaries, and the motion of ships at sea have been subjected to experimental research, it appears impossible to assign a limit to the range of experiments as a means of extending engineering knowledge. The correct calculations of strains, the exact strength of materials, and a strict appreciation of the physical laws affecting designs are of the utmost importance, and the failure of many bridges might be explained by a neglect of these considerations. Occasionally failures of works might be attributed to exceptional causes or peculiarly unfavorable conditions, but in most cases they are the result of errors or deficiencies in design which might have been avoided by a more correct appreciation of the physical conditions involved.
Electrical Effects of Spray.—A correspondent, writing to us concerning the effect of various atmospheric conditions on health and bodily vigor, cites his own experience in a fire brigade as having led him to believe that deficiency of ozone and other unfavorable conditions and the effect of atmospheric impurities may be alleviated by inhalation through a spray of cold water. A method of ventilation of railroad cars which was very comfortable to passengers riding in cars so treated, but has been disused, depended upon the application of this principle. Its value is further confirmed by what Prince Kropotkin has said in one of his recent articles on current science concerning the theory of the development of electricity by spattering water. A few years ago Herr Lenard undertook a series of observations in Switzerland on the electrical effect of waterfalls. It appeared that even small cataracts, only a few feet high, send into the air considerable charges of electricity, provided they bring down a large amount of rapidly dashing water. The smallest jets of water that drip on the rock sides, and even roaring streamlets, have the same effect. He suggested that the chief cause of electrification is the tearing asunder of the drops of water as they fall on the wet surfaces at the bottom of the waterfall. The experiments on which these views are founded accord with the demonstration by Lord Kelvin and Messrs. Maclean and Goto that air, even absolutely dust free, can be electrified by a jet of water. This source of electrification is further shown to be by no means insignificant, and the amount of electricity sent into the air in this way is immense. The importance of these facts in the economy of Nature, says Prince Kropotkin, is self-evident. "The supply of electricity in the air is continually renewed. The waterfalls in the valleys, the splashing of the waves on the shores of lakes and rivers, and the splash of drops of rain on the ground send masses of negative electricity into the air; even the watering of our streets and of our plants in the orchards has the same effect on a limited scale. On the other side, the waves of the sea, as they break against the rocks and fall back in millions of droplets upon the beach, supply the air with masses of positive electricity the amount of which rapidly increases after each storm. And when we stand on a sea beach we not only inhale pure ozonified or iodized air; we are, so to say, surrounded by an electrified atmosphere, which, as already remarked by Humboldt and often confirmed since, must have a stimulating effect upon our nervous activity as well as upon the circulation of sap in plants."
The Sciences Auxiliary to Engineering.—Among the branches of science necessary for the engineer, Mr. L. F. Vernon Harcourt, in his address at the British Association meeting, named mathematics and physics as of the highest importance, and as those upon which the profession mainly depends. Other sciences of considerable though comparatively minor importance are those of chemistry, meteorology, and geology. All branches of applied mathematics have to be used by engineers, or, as in the case of several general principles and tidal calculations, by mathematicians, for their benefit; but graphic statics will probably gradually supersede analytical methods for the calculation of stresses, as more rapid and less liable to errors, which are also more easily detected in graphic diagrams Pure mathematics, in its higher branches, appears to have a less direct connection with engineering; but applied mathematics is so largely dependent upon pure mathematics
