BAR ther. Even prior to that date, namely, in 1643, experiments were instituted, both at Florence and Rome, with the Torricellian tube ; and in 1(548 Perirr, a French- man, made use of two similar in- struments ; one of which he left in a valley, while with the other he ascended one of the highest mountains of Auvergne; and thus he observed, that the atmosphere 0:1 the top of the hill did not press upon the mercury with a force equal to that observed in a lower situation, where he found the quicksilver much lower than in the former region; and hence he judiciously concluded, that the air must be lighter, or more rarefied, in proportion to the altitude of places. But that these remarkable changes were in any degree con- nected with the present, or fu- ture, constitution of the weather, was doubdess discovered by Gue- Ricke, though Mr. Boyle, whose talents and genius deserve the highest admiration, improved and applied it to philosophical purposes. This assertion is amply supported by a passage in a printed work still extant, and entitled "Casp. Schotti Technlca curiosa" (ii. 22. p. 52) ; by which it appears, from a letter addressed to the author by Gue- ricke, that the latter had con- structed a tube filled with mercury, on the top of which fluid he placed a small wooden figure, that rose and fell with the quicksilver, point- ing out with its finger, or index, the variations in the gravity of the air, and at the same time the con- comitant changes of the weather. The compound barometer, the tube of which is filled not only with mercury, but likewise with another coloured fluid, was in- vented by Carte sius and Hwir- HO. II, VOL. I. BAR r<7? gens, much about the same time ; but the latter considerably im- proved it, by using a double tribe, and mixing the water with orie- sixth part of aqua-fords, to pre- vent its congelation in winter. The conical or pendent baro- meter was contrived by M. Amox- tons; the well-known diagonal barometer, by Sir Samuel More- land; the wheel barometer, by Dr. Robert Hooke, who like- wise improved Huygens's double barometer above-mentioned ; — -the 1 rectangular horizontal barometer was invented by Bernouilli, or rather Cassini ; and the. credit of another invention, by which four tubes (containing mercury, and a lighter fluid alternately) are con- nected together, is likewise due to Amontons. The marine barometer was also invented in the beginning of the 18th century, by Dr. R. Hooke, and afterwards rendered more perfect by M. Passement, who, by the simple, but effectual ex- pedient, of twisting the middle part of die common, or Torricel- lian tube, into a spiral of two revo- lutions, prevented the oscillations of the mercury on ship-board. By this ingenious contrivance, the shocks which die mercury sustains from the motions of a ship, are ef- fectually broken; as, from the turns of the instrument, the im- pulses are transmitted in contrary dire£tions. But of all the instruments con- trived for the purpose of ascertain- ing tire specific gravity of the at- mosphere, diat of Magellan, in the year IJiiG, deserves a distin- guished nlace; as it points out not only the changes occurring in the atmosphere, but likewise, and in a very sensible manner, the dif- N terent
