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his Fundus subterram, and improved and first brought into use here, divers years agoe, by the Noble R. Boyle, who also, as himself informed the Publisher, hath in some of his Writings, yet unpublisht, set down a full Description thereof.
It is such a Glass-Tube as is represented by Fig. 7. blown at a Lamp, and poised in good common Water by putting Quick-silver into it, until it sink so low, that nothing appear above the Superficies of the Water, but the Top; which done it is to be
sealed up, and to be graduated on its side, into what parts you
please; which may be done with a Diamond. And then, being
put into any Water to be weighed, it will, by its more or less
sinking into it, shew the differences of the Waters gravity.
To perform this, let there be made a Square Wooden Bucket (such as C in Fig. 8.) whole bottoms E E are to be so contrived, that the weight A do sink the Iron B (to which the Bucket C is fastned by two Handles D D, on the ends of which are the moveable bottoms or Valves E E) and thereby draws down the Bucket, the resistance of the Water keeps up the Bucket in the posture C, whereby the Water hath-a-clear thorow-passage all the while it is descending; whereas as soon as the Bucket is pulled upwards by the Line F, the resistance of the Water to that motion, beats the Bucket downward, and keeps it in the posture G; whereby the included Water is preserved from going out, and the Ambient Water kept from getting in.
By the advantage of which Vessel, or such like, you may come
to know the Degrees of Saltness of Sea-Water, according to its
nearness to the Top or Bottom; or rather, the Constitution of the
Sea-Water in several Depths of several Climates: Likewise,
whether in some places of the Sea, there be any sweet Water at
the Bottom; the Affirmative whereof is to be met with in the
East-Indian Voyages of Van Linschoten, who pag. 16 of that
Work, as 'tis Englished, records, that in the Persian Gulf, about
the Isle of Baharem, fetch up with certain Vessels (which he
de-
