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288 observers in connection with the work in question, and the measures now published not only confirm this favourable opinion of the instrument, but bear inherent testimony to the care and patience expended on the observations, and will doubtless be received as an important and valuable contribution to double-star astronomy, and especially by those who are ripe with similar observations, or the investigation of the orbits of the binary systems. Amongst the more interesting of the revolving stars, the Catalogue has measures of η Cassiopeæ, 36 Andromedæ, α Geminorum, ζ Cancri, ω Leonis (which difficult object was just divided at the end of March 1873), ξ Ursæ Majoris, Υ Virginis, ξ Bootis, η Coronæ, Σ 1938, ζ Hereulis, 70 Ophiuchi, Σ 3062, &c. The interesting, though difficult binary Σ 518 (Eridani), is probably within the power of such an instrument, but does not appear in the Catalogue; it may be suggested that it is not too late to examine this object in the present season, the actual angle may probably be found very considerably in advance of that obtained by Prof. Winnecke in 1864, and a first approximation to the form of the orbit may soon be practicable.

.—If we take a mean of the measures of the diameters of the satellites by Struve at Dorpat, and by Engelmann at Leipsic, we shall have for apparent diameters at the mean distance of the primary:— I. … 1"·048 II. … 0"·911 … III. 1"·513 … IV. 1"·278 and with a solar parallax of 8"·875, the true diameters in English miles will be:— I. … 2,435 … II. 2,115 … III. 3,515 … IV. 2,970 The angular diameters at the centre of Jupiter, are:— I. … 31'·4 II. … 17'·1 III. … 17'·8 IV. … 8'·6 and the mean distances from the centre of Jupiter:— The diameter of the planet’s equator is assumed to be 88,200 miles, as lately given in this column.

THE DRAINAGE OF THE ZUYDER ZEE

HE Dutch are a people who in many respects command the respect of the world. Their little country possesses comparatively few natural resources, and yet they have made so much of it, and they have been compelled to cultivate the virtues of frugality and industry to such an extent, that the people as a whole are probably better off than those of any other country in the world. Small as the country is, it is only by the exercise of great skill and constant watchfulness that they are able to prevent its being overwhelmed by the German Ocean. In this unfortunately they have not always been successful. Over and over again has the sea burst in upon them, laying waste their dearly-loved country, and sweeping away thousands of the inhabitants. It has only been after many severe lessons that they have learned how to keep the invader back. And within recent years they themselves have taken the offensive, and determined to drive out old Neptune from lands which he has possessed for centuries. Even in the seventeenth and eighteenth centuries they succeeded in draining many small areas of land, and during the present century many marshes and lakes have been brought under cultivation, including Lake Haarlem, upwards of 40,000 acres in extent, In this way about 350 square miles of land, mostly devoted to pasture, have been reclaimed, and that entirely by means of windmills,

Now, however, that the applications of steam-power have reached such perfection, this enterprising people have determined upon an enterprise much more gigantic than any they have hitherto attempted,—nothing less than the drainage of the Zuyder Zee. Until the end of the thirteenth century the area now occupied by that arm of the ocean seems to have been mostly dry land, with a Lake in the centre, which by means of a river drained into the German Ocean. At the time mentioned, however, in 1282 according to some authorities, the sea broke through what is now the Strait of Helder, and converted the dry land into a gulf.

For many years the drainage of the Zuyder Zee has occupied the attention of the Dutch Government and of engineers, but it is only since the improvements in the application of steam that the idea has been seriously entertained. At last a scheme has been adopted, after many years’ careful research and consideration, for the details of which we are indebted to the French journal L'Explorateur.

As early as 1865 a Dutch Credit Foncier Association took up the scheme at the suggestion of Mr. Rochussen, an eminent statesman, and employed two engineers, M. Beijerinck, who drained the Haarlem Lake, and M. Stieltjes. These reported on the practicability of draining the southern, the shallowest and most fertile, half of the inland sea. Soundings were made, and numerous specimens of the bottom brought up, and in short a thorough investigation made from a geological and agronomic point of view. The result of these investigations was most favourable, and the specimens submitted to the analysis of a distinguished agricultural chemist, M. van Bemmelen, having been found to consist of alluvial clay or loam of the first quality and of great depth, over an extent of four-fifths of the bottom of the sea, the Society entered into negotiations with the Government. A Government Commission was appointed to consider the whole question from an economic and scientific point of view, and after an investigation lasting about two years, gave in their report in April, 1868. This report was in favour of granting a concession to the Credit Foncier, whenever that company could present a definite plan that would obviate all existing objections. The Society, after further consideration, requested the Government to delegate a commission of specialists to report further on the scheme, taking into consideration all the interests concerned, and to decide upon the plan best adapted to carry the scheme into execution. After three years thorough consideration the Commission gave in a voluminous report in April 1873, which declared that the project from an engineering point of view was practicable; that the clearing of the new lands would be a difficult and very expensive enterprise, but that the experience acquired and the progress of science would furnish the means of overcoming these difficulties, and of making the enterprise a benefit to the country.

The drainage will be effected in that part of the gulf lying between the provinces of Guelderland, Utrecht, and North Holland, over an extent of 195,300 hectares (about 740 square miles, nearly equal to the area of Surrey, and about 100 miles larger than the Dutch province of Zeeland), by means of a principal dike or embankment, of 40 kilometres in length, 50 metres broad at the base, and raised 5 metres above the ordinary tides, to be constructed from the left bank of the mouth of the Yssel to the island of Urk, and from hence to the town of Enkhuyzen in the province of North Holland. The inclosed area will be divided into squares, and numerous pumping steam-engines will then be set to work, having a collective force of 9,400-horse power. The Commission estimates that the work will be entirely accomplished in sixteen years, and that it will cost a sum of 10,000,000l., not including the interest of the capital employed; or 1,600,000l., for preparatory works, provisional circular canals, &c., about 2,760,000l., for the construction of the dike, and the rest for the purchase of engines, the drainage proper, and the construction of reservoirs, internal canals, roads, railway