In an interesting report on the "Waterstaat" of the Netherlands, presented to the British Government, we read: "To appreciate the beauty of the Dutch science of hydrodynamics, it is necessary to understand that, from first to last, it is a question of comparative levels. The error of a centimÈtre in level might drown a province, or frustrate the purpose for which some canal had been designed. Thus it may be said, without exaggeration, that the most important institution in the kingdom of the Netherlands is a certain antiquated pile at Amsterdam—but one of many million pine-trees brought from Norway, on which the city is perched,—which indicates the rise and fall of the outer waters of the Zuyder Zee and German Ocean. For 200 years this pile has been watched with anxiety by the burghers of the Netherlands, and a graduated scale has been marked upon it, in which the mean water level is represented by zero. It is known as the 'Amsterdamsche Peil,' and every hydraulic undertaking in the country is measured by its standard, as having a level of so many mÈtres or centimÈtres above or below the usual level of the sea. The initials A. P. (Amsterdamsche Peil), O. A. (Zero of Amsterdam), or Z. P. (Zero of Pile), are the forms of abbreviation most generally used to represent the starting-point in all hydraulic calculations; and one of these, with the signs + and -, must therefore necessarily occur in every intelligible description of Dutch public works."