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where V is the unknown velocity of the wind, a and x two constants which are to be determined. Each observation gives two equations in which there are four unknown quantities, for it is found that the value of V changes from one instrument to another; this is partly owing to eddies caused by the buildings, but also in great measure to the irregu larity of the wind itself. It is, however, also found that these wind-differences are as likely to have + as signs, and therefore it may be expected that their sum will vanish in a large number of observations. The ordinary methods of elimination fail here even to determine with precision a single constant, and Dr. Robinson therefore proceeded by approximations. He tried five different types of anemometers, and obtained very unexpected results, for he found that the a varied as some inverse function of the diameter of the cups and the arms. He gives its values:

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No. 6 is similar to No. 2, and it might be expected that their constants would be equal. The cause of these differences is partly the eddies caused by the cups which are more powerful when the arms are short, but still more the presence of high powers of the radii and diameter occurring in the expressions of the mean pressures on the concave and convex surfaces of the hemispheres. In the present state of hydrodynamics we cannot assign these expressions, but we know enough to see that such powers may be present.

As each type of anemometer has its own constants, the author would suggest to meteorologists the propriety of confining themselves to one or two forms. For fixed instruments he considers the Kew as good as any, and would wish to see it generally adopted. For portable ones he has no experience except with Casella's 3-inch cups, 6-inch arms, which he found very convenient; he has not, however, determined its constants. Some selection of the sort seems necessary if it is wished to have a uniform system of wind-measures. (Nature, XXII, p. 404.)

An unpublished investigation of the accuracy of the Kew anemometers was made by Messrs. S. Jeffoy and G. M. Whipple about 1873 at Kew and the Crystal Palace. These observations have been discussed by Prof. G. G. Stokes, who concludes as follows:

"1. That at least for high winds the method for obtaining a factor for an anemometer which consists in whirling the instrument in the open air is capable, with proper precautions, of yielding very good results.

"2. That the factor varies materially with the pattern of the anemom.

eter. Among those tried, the anemometers with the larger cups regis tered the most wind, or, in other words, required the lowest factors to give a correct result.

"3. That with the large Kew pattern, which is the one adopted by the Meteorological Office, the register gives about 20 per cent. too much, requiring a factor of about 2.5 instead of 3. Even 2.5 is a little too high, as friction would be introduced by the centrifugal force beyond what occurs in the normal use of the instrument.

"4. That the factor is probably higher for moderate than for high velocities; but whether this is solely due to friction the experiments do not allow us to decide.

"The problem of the anemometer may be stated to be as follows: Let the uniform wind with the velocity V act on a cup anemometer of given pattern, causing the cups to revolve with a velocity v, referred to the center of the cups, the motion of the cups being retarded by a force of friction F; it is required to determine v as a function of V and F, F having any value from 0, corresponding to the ideal case of a frictionless anemometer, to some limit F1, which is just sufficient to keep the cups from turning. I will refer to my appendix to the former of Dr. Robinson's papers (Phil. Trans., 1878, page 818), for the reasons for concluding that F is equal to V2, multiplied by a function of V÷v. Let V÷v=5, F ÷ 27, then if we regard and as rectangular co-ordinates, we have to determine the form of the curve lying within the posi tive quadrant On, which is defined by these co-ordinates.

"We may regard the problem as included in the more general problem of determining v as a function of V and F where V is positive, but F may be of any magnitude and sign, and therefore v also. Negative values of F mean, of course, that the cups, instead of being retarded by friction, are acted on by an impelling force, making them go faster than in a frictionless anemometer, and values greater than F, imply a force sufficient to send them around with the concave sides foremost." (Nature, July, 1881, XXIV, p. 253.)

C. E. Burton describes as follows an integrating anemometer that gives the quadrantal components of the movement of the wind: "A roller with a spherical edge is made to revolve with a velocity proportional to that of the wind as recorded on an anemogram. This roller presses on a plane table carried by two mutually perpendicular pairs of rails in planes parallel to that of the table. The lowest of the pair of rails is supported by a frame carried on the extremity of a vertical shaft. The point of contact of the roller with the table lies in the prolongation of the axis of the shaft. The table can rotate with the shaft, but not independently. By a simple arrangement the shaft and, consequently, the table are caused to take up positions corresponding from moment to moment with the direction of the wind-record on the anemogram. A style concentric with the shaft presses lightly against a compound sheet of tracing and carbonized paper attached to the under side of the table.

Arrangements are also made for obtaining the sum of the movements of the table toward each of the four cardinal points. If the roller be moved with a velocity proportional to that of the wind, whether directly by a cup anemometer or by a mechanical translation of the trace as given by such an instrument, while the table simultaneously assumes orientations corresponding to the direction of movement of the air, the line drawn by the style will be a miniature copy of the path of an imaginary particle animated by the movements actually belonging to the masses of air which successively affect the anemometer at the given station during the selected period, rigorously in accordance with the principle known as Lambert's." (Nature, October, 1881, XXIV, p. 583.) H. S. Hele Shaw and Dr. Wilson have invented a new integrating anemometer. An ordinary Robinson's cup anemometer is used to drive a train of wheels, and thus ultimately a serrated roller, which moves a board in the direction of, and with a velocity proportional to, that of the wind. On the board, which is horizontal and about two feet square, is placed a sheet of paper, upon which the roller presses, and in turning leaves the required trace, at the same time moving the paper underneath it. The board is prevented from having a rotary motion by means of a pair of frames, the upper moving by means of wheels on the lower, each of which can move only in one direction, and these directions are perpendicular to each other. By a clock-work adjustment the time element is able to be introduced, which, taken in connection with space, gives velocity. (Nature, September, 1881, XXIV, p. 467.)

Messrs. Burton and Curtis have published the result of a series of observations on the distribution of pressure over the surface of a flat plate exposed perpendicularly to the action of the wind. They obtain this distribution by inserting on the rear of this plate a number of small Pitot's tubes, each of which gives the pressure for its own location. They find, of course, the maximum pressure at the center diminishing to scarcely one-half of that near the edge of the plate, the rates of dimi nution varying with the size and shape of the plate. (Nature, XXV, p. 427.)

Ventosa describes an integrating anemometer invented by himself very nearly identical with that proposed by Shaw and Wilson, and simpler than that of Von Oettingen. (Nature, XXV, p. 79.)

Bourdon describes to the Paris Academy of Sciences a new form of multiplying anemometer. His system consists of convergent divergent tubes. In one such tube, made according to Venturi's proportions, is fixed concentrically a second, much smaller, and having its divergent end exactly at the point where the truncated summits of the cones of the larger tube unite. (For very small velocities a third tube may be similarly fixed within the second.) A hollow sleeve is fixed round the union of the truncated cones of the wide tubes; its interior communicates with that of the latter and with a manometer, on which the pressure is read. If a manometer at the mouth of the large tube register 1

with a current, the other manometer will register, e. g., 6; the pressure here is negative, and due to acceleration of the velocity of the current. (Nature, XXV, p. 356.)

Prosser having exhibited a drawing of the anemometer of D'Ons en Brays at the anemometer exhibition of the London Meteorological Society, under the impression that it was the earliest self-registering anemometer, also gives in Nature, Vol. XXV, page 505, references to the anemometer invented by Sir Christopher Wren, as described in Birch's History of the Royal Society, published in 1663. (If we combine his references with the description of an anemometer given in Sprat's History of the Royal Society, London, 1667, we must be convinced that to Sir Christopher Wren is due the invention of that form of anemometer that has of late years frequently been styled Wild's tablet anemometer; indeed, to him seems to be due almost wholly the early stimulus given to meteorological observations in England.) Prosser also refers to the famous paper by Edgeworth on the pressure of the wind upon surfaces of different forms, published at page 136, Phil. Trans. for 1783.

In order to avoid the assumptions that seem necessary in reducing ordinary anemometric observations at sea, Abbe has proposed to establish at various parts of a vessel triple anemometers, recording respectively the three vertical and horizontal rectangular components of the compounded motions of the wind and the instruments. As a first step in this investigation, three anemometers were, in October, 1882, set up at different points on the steamship Ohio, and observations kept up by Mr. Frank Waldo between Baltimore and Hamburg.

Mr. W. Bailey exhibited to the Physical Society of London on the 10th of June a model of the new integrating anemometer. The disk is revolved by means of Robinson's cups. (Nature, XXVI, p. 167.)

The brothers, Brassart, of Rome, philosophical-instrument makers, have devised a simple inexpensive anemoscope and anemometer, about forty of which are now at work at various Italian stations. (Nature, XXVI, p. 511.)

MM. Mignan and Ranard have constructed an integrating hygrometer for precipitating the vapor of the atmosphere, and analyzing the products, if required. It is composed of an iron tube, filled with liquor ammoniæ; by gently opening a tap the ammonia is absorbed by water, and the hygrometer is covered with moisture, which is collected in a cup arranged for the purpose. During the recent dry weather the amount of precipitation was 3 grams of water in twenty minutes. The weight of liquor ammonia was 34 grams. A peculiarity is that a number of floating particles are precipitated with the humidity of the air. It has been suggested by M. W. de Fonvielle that the hygrometer might be used for analyzing the matter of clouds where the precipitation of a few grams will be a question of a very few minutes. (Nature, XXV, p. 565.)

Crova describes a new condensation hygrometer. A small tube of

nickel-plated brass, carefully polished within, is closed at one end with ground glass, and at the other with a lens of long focus, through which one looks along the tube towards a source of light. Through two parallel tubulures the air to be examined is drawn into the tube, which is cooled by means of sulphide of carbon traversed by an air current in a metallic envelope round the tube. The changes of aspect in the tube at the temperature of saturation enable one to estimate the dewpoint to one-tenth of a degree. (Nature, XXVI, p. 168.)

J. F. D. Donnelly calls attention to the recent perfections introduced into the spectroscope by Mr. Hilger, who has managed to secure increased dispersion and an excellent vision of the so-called rain band; the spectroscope is also fitted with a telescope and with a second object glass in front of the slit, for the purpose of bringing light from external objects to a focus on it. (Nature, XXVI, p. 501.)

The Comité International, representing several countries of Europe, the United States, and South America, has published an important volume of memoirs by Drs. Broch, Pernet, René-Benoît, and Marek, on subjects relating to the determination of units of measure and weight.

As the intensity of weight varies with the geographical height and position above sea-level, the committee give in their first memoir tables of the ratio of acceleration of weight at the level of the sea for different latitudes to its acceleration at latitude 45° (Paris), to which latitude they recommend that all weighings be referred.

In the second memoir, which relates to the tension of aqueous vapor, certain corrections of hitherto accepted results are also indicated, particularly the errors of calculation in Regnault's tables, as shown by Moritz, and new tables are given for tensions at all temperatures on the new scale of normal degrees from 30° to +101° C.

With reference to the fixed points of mercurial thermometers, the Comité adopted the proposition that the point 0° of the centigrade thermometer should be fixed at the pressure of 760mm, when determined in 45° latitude and at the mean level of the sea. Also at the Congress of Meteorologists at Rome, in 1879, there was adopted the proposition of Dr. Pernet to fix the boiling point of water, 1000 C., under the above pressure, so as to render strictly comparable the temperatures observed at different places. Degrees of temperature between these points are called normal degrees.

Tables are also given by which may be calculated the weight of a liter of pure air in different latitudes and at different altitudes. In London (latitude = 51°30', 51° 30', altitude 6.7m.) the weight is 1.2938 grams. (Nature, August, 1881, XXIV, p. 384.)

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Schloesing, as the result of experiments on the absorption of volatile bodies with the aid of heat, is led to propose the application of his method to the determination of the quantity of nitric acid in the atmosphere. (Nature, XXVI, p. 24.)

Mr. C. V. Boys read before the Physical Society, London, a paper on the

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