zontal dimensions. These clouds play the part of humid conductors, connecting inferior with superior strata; and their dissolution, in the form of rain, is connected with electric phenomena.

Meteors and Zodiacal Light.

Although meteors are to be considered as proper subjects of study for the astronomer, yet often, by their entry into the earth's atmosphere, they come to have a special interest for the meteorologist. The phenomena shown by their trains. have not yet, that we are aware of, been subjected to any comprehensive study during the past few years; but the important question as to the amount of heat introduced into our atmosphere by the destruction of a part or all of the vis viva of all the meteors that enter therein has been taken up by Govi, who finds that modern discoveries serve to abundantly elucidate the subject. It is not, however, likely that the temperature of the lower layers of the air is sensibly af fected by this source of heat.

Dr. G. von Niessl communicates to the Astr. Nach. the results of a preliminary investigation into the Daily Variation of the Shooting-stars, in which he shows that numerous conclusions deduced from a careful consideration of the theory of the nature and movements of these bodies do not agree sufficiently well with the observations of the past few years; and he suggests that the true explanation lies in the following assumptions: first, that the density of the perihelia of the meteoric orbits diminishes with increasing perihelion distance; second, that the orbits are much more frequently hyperbolic than parabolic.

Some instructions for the observation of Zodiacal Light are given by Serpieri, in the "Meteorologia Italiana" for 1878, in which he calls special attention to the points observed by the Rev. George Jones, and also by Heis and Schiaparelli. Some connection between the zodiacal light and the aurora seems also to be indicated by the observations of Bruno at Mondovi, February 4, 1872.

In Vol. XXV. of the "Memoires Couronnés" of the Royal Belgian Academy, Houzeau gives a Summary of Astronomical and Meteorological Observations made by him in the tropics and adjoining portions of the temperate zone. His observations included the zodiacal light, which was seen on

56 days out of 179. This series is of remarkable accuracy and import, and demonstrates that the zodiacal light is in the plane of the ecliptic without sensible deviation therefrom. The meteorological observations consist of five years. of records at 6 A.M., noon, and 6 P.M., near Kingston, Jamaica, West Indies. Among the remarkable phenomena he notes rain from a cloudless sky for 13 consecutive hours.

Professor Everett publishes in the Proceedings of the Belfast Society a lecture delivered by him Jan. 22, 1878, on Atmospheric Electricity. He sums up our knowledge as follows: "There is no other meteorological element, except perhaps the wind, that can compare with electrical potential for the extent and suddenness of its variations. On some rare occasions, with no assignable external cause, and notwithstanding the mitigating action of the collector, which eases off all sudden changes, the needle of the electrometer swings from side to side with a violent trembling like that of a magnetic needle in a strong field. As regards the variation of potential according to the season of the year, all observations concur in showing that the average strength of potential is greater in winter than in summer, but the months of maximum and minimum appear to differ considerably at different. places. The chief maximum occurs in some one of the winter months; the chief minimum occurs everywhere in May or June; the average potential in the strongest month is about double of that in the weakest. As regards the variation of potential with the hour of the day, the Kew observations show a double maximum in the twenty-four hours. The hours of maximum are, in July, 8 A.M. and 10 P.M.; in January, 10 A.M. and 7 P.M.; and in the spring and autumn, about 9 A.M. and 9 P.M. The few observations taken during the recent Arctic expedition show that the general features of atmospheric electricity were the same at the winter-quarters of the Alert as they are in these temperate regions." He adds that our great want at present is balloon observations, and suggests a method by which such can be made. With regard to the origin of atmospheric electricity, he says: "I feel convinced that friction either of the air itself or of the solid or liquid particles contained in it against the surface of the earth is one cause of the generation of electricity in the air."

PHYSICS.

By GEORGE F. BARKER,

PROFESSOR OF PHYSIOS IN THE UNIVERSITY OF PENNSYLVANIA, PHILADELPHIA.

GENERAL.

The year 1878 has witnessed a considerable progress in the science of Physics. A noteworthy occurrence is the address delivered at Glasgow, by Dr. C. W. Siemens, "On the Utilization of Heat and other Natural Forces," because he discusses in it the available sources of power when the supply of coal shall fail. Using at some central station water- or windpower to drive dynamo-electric machines, the current generated could easily be reconverted into power where it is wanted, either for mechanical or other purposes. For light, for example, from 100 horse-power 125,000 candle-lights would be obtained, equivalent to 6250 Argand burners of 20 candles each, consuming six feet per hour, or 37,500 cubic feet for all. To produce this amount of gas, 3 tons of coal are required, while to produce the 100 horse-power only as many hundred-weights are necessary. In the case of Niagara, he computes that 100,000,000 tons of water fall every hour through a vertical height of 150 feet, giving 16,800,000 horse-powers, the only result being an elevation of the temperature of the water by one fifth of a degree Centigrade. To pump back the water would require an annual expenditure of 266,000,000 tons of coal (at four pounds coal per horse-power per hour)-an amount equal to the total coal consumption of the world. Since by electric means one half the energy supplied at the central station may be recovered at the distant one, the economy is greater than in the steam-engine. Greater care in the use of water- and wind-power is now possible, and the intermittent character of wind-power may be made permanent by using it to raise water into a reservoir. Moreover, the force of falling water in its descent from reservoirs and lakes, to supply our large cities, might be utilized on the way by driving turbines,

thus supplying light and mechanical power as well as the

water.

Wild has communicated to the St. Petersburg Academy of Sciences an important metrological paper, in which he describes his new linear comparator, and gives the results of his examination with it of a normal meter made by Hermann & Pfister, of Berne. The new comparator reads to 0.0001 millimeter and to 0.01 of a degree Centigrade. The true length of the normal meter was found to be 999.9838 millimeters, with a probable error of ±0.00026 millimeter. Wild also discusses the desirability of quartz in the form of rockcrystal as a material for standards, especially for linear units, and gives his opinion strongly in its favor. A spherical or cylindrical standard hectogram of this material, or a standard divided decimeter, can now be had of Stein, in Oberstein, for thirty thalers. A simple and excellent method of reading the deflection in balances of great precision, by means of a mirror with its telescope and scale, placed at a distance, is also given.

The mathematical treatment of the problems arising from. the motions of bodies confined to the surface of the rotating earth has been treated of by Bertram in an inaugural dissertation at Marburg, on the motion of a material point upon surfaces of rotation; and by Suttor, of the Royal Institute at Luxembourg, on the movement of bodies on the surface of the earth, etc. The former author confines himself to the elaboration of very general mathematical formulæ for rotating cylinders, paraboloids, spheres, etc. The latter author gives more special formulæ, deduced from Corioli's propositions, and shows their adaptation especially to the vibration of pendulums, and the experiments of Foucault on the rolling of spheres down inclined planes, and the fall of bodies, as in Reich's experiments at Freyberg.

Jewell has described in Nature a new form of sinker for deep-sea sounding, in which certain objections to the sinker of Sir William Thomson are obviated. An iron casting five inches in diameter at the top and three at the bottom, and 26.5 inches long, is cast with a cylindrical cavity two inches in diameter, extending from the top to within an inch of the base. A glass tube forty-eight inches long is closed at one end and bent so as to produce a U tube twenty-four inches.

long. This is placed in the cavity in the sinker with the bend upward, and of course the closed end downward. The whole is supported by a swivel-link at top. When immersed, the air in the tube will be compressed, and at a depth of five and a half fathoms the water will rise in the open leg to the bend; any further descent will cause it to flow over into the closed leg. By calibrating and graduating this leg, the amount of water which it contains when raised will, of course, indicate at once the depth to which it has descended. If desired for use in water shallower than five and a half fathoms, the open leg may be made shorter than the closed one.

MECHANICS.

1. Of Solids.

In Mechanics Abbot has repeated and extended his experiments to determine the velocity of transmission of earth waves caused by explosions, in order to settle certain questions raised by Mallet. He concludes: 1st. That a high magnifying power of telescope is essential in seismometric observations. 2d. The more violent the initial shock, the higher is the velocity of transmission. 3d. This velocity diminishes as the general wave advances. 4th. The movements of the earth's crust are complex, consisting of many short waves first increasing, and then decreasing in amplitude; and with a detonating explosive, the interval between the first wave and the maximum wave at any station is shorter than with a slow-burning explosive. The seismometer used was a dish of mercury, whose surface was watched through a telescope, by which the beginning and duration of the tremor could be determined. The velocity observed was for short distances 8500 feet, and for long 5300 feet per second.

Cornu and Baille have continued their experiments on the determination of the density of the earth by the method of Cavendish, and have considerably improved their apparatus. They have quadrupled the force to be measured by increasing the attracting spheres of mercury from two to four, and by diminishing the distance through which the attraction is exerted in the relation of √2 to 1. With these improvements, the results are completely uniform, so much so that