“It is impossible,” says he, “that the _hydroscopium_ could be the level or _chorobates_ of Vitruvius, for the lines on the latter were perpendicular to the horizon, whereas the lines on the former were parallel to it. The hydroscopium was undoubtedly a hydrometer of the simplest construction. The tube may be made of copper, and open at the top; but at the other end, which, when used, is the lowest, it must terminate with a cone, the base of which is added to that of the tube. Lengthwise, along the tube, are drawn two lines, which are intersected by others, and the more numerous these divisions are, the instrument will be so much the more correct.--When placed in water it sinks to a certain depth, which will be marked by the cross-lines, and which will be greater, according to the lightness of the water.” A figure which is added, might have been dispensed with. When a common friend of Fermat and Petau showed it to the latter, he considered it to be so just, and explanatory of the real meaning of Synesius, that he wished to be allowed the opportunity of introducing it in a new edition of the works of Synesius. _FINIS._ J. S. Pratt, Stokesley, Yorkshire. Transcriber’s Notes Punctuation, hyphenation, and spelling were made consistent when a predominant preference was found in this book; otherwise they were not changed. Many typographical errors were corrected; occasional unbalanced quotation marks retained. Text uses both “Guttenberg” and “Guttenburg”, “Helvelius” and “Hevelius”; both versions retained. Page 18: “documentary” was printed as “documentry”; changed here. Page 33: “transcendant” was printed that way. Page 33: The opening quotation mark preceding “A complete Course of Lithography” was added by Transcriber. Other punctuation and spelling within that title has not been changed, but some of it differs from what was printed in the English translation of the cited book. Page 54: The period after “Deity” in “offensive to the Deity. that the great majority” probably should be a semi-colon. Pages 63 and 249: A question mark is followed by a lower-case word. Page 109: “Chardiu” was printed that way. Page 139: “It last it changed colours” should begin with “At”. Page 171: “the bull of Æolus” probably is a misprint for “ball”. End of the Project Gutenberg EBook of A Historical Account of Useful Inventions and Scientific Disc, by George Grant