BAR 



286 



BAR 



Biro?.c!i. still employ its inhabitants. Number of houses 619. 

 Population 31-78, of whom "S were returned as em- 

 ployed in trade. See Oldfield's History of the Bo. 

 roughs. ( j ) 



BA ROACH, Broach, Barokia, or Baruk, 

 the Barygajutk of the ancients, a town of Himlos- 

 tan, in the province of Guzerat, situated on a ri- 

 sing ground surrounded with water, on the river Ner- 

 buddah, near the place where it falls into the Gulf 



of Cambay. A factory was established hero in Baroaci. 



HJ16 by the English; and in Ki83 it had flourished ' / 



to such a degree, that no less than SSfiOO pieces of 

 baftacs, &c. of different kinds, manufactured i,i the 

 neighbourhood, and superior to those of Bengal, were 

 shipped for England. Agates, found in the mountains 

 near Brampour, also form one of the articles of 

 trade. East Longitude 72 5V, North Latitude 21 a 



BAROMETER. 



Barometer. Barometer (compounded of /Sxgoi weight, and ft&T on 

 v measure,) is an instrument for determining the weight 



History. of the air, and the variations of its pressure in diffe- 

 rent circumstances. As every change in the weight 

 of that fluid is accompanied with corresponding 

 changes of density, and consequently of its disposi- 

 tion to absorb or deposit moisture, the barometer is 

 also employed to point out the probable changes of 

 weather ; hence it is not unfrequently called a xisea- 

 iher-glass. ( See Meteorology. ) Another purpose, 

 scarcely less important, to which this instrument has 

 lately been much applied, is the measurement of acces- 

 sible heights ; and the results obtained by means of 

 it approach so near to perfect accuracy, when all cir- 

 cumstances are properly estimated, that this method 

 of determining the heights of mountains is, in many 

 cases, even preferable to the geometrical methods. 

 ( Sec Heights.) It also appears from the observations 

 of Captain Flinders, that the barometer may be of the 

 most essential service at sea, not only to foretel changes 

 of weather, but also to indicate the vicinity of land. 

 (See Winds.) These important properties entitle this 

 instrument to a considerable share of our attention. 



Before the discovery of the weight of the air, the 

 barometer was entirely unknown ; and indeed it was 

 the discovery of that fact, which led to the invention of 

 the instrument. The ancjents ascribed to the horror 

 of a vacuum all the effects which arise from atmo- 

 spherical pressure. This explanation, absurd as it may 

 now seem, was admitted even by Galileo ; and the in- 

 genuity of a Pascal and a Boyle was scarcely sufficient 

 to point out its futility, and banish it from the esta- 

 blished principles of philosophy. The influence of 

 occult qualities, was, in all difficult cases, assumed to 

 explain the phenomena of nature, and it was less in- 

 consistent with their prejudices to ascribe the effects 

 of the weight of the air to an invisible agent, or an 

 unknown principle, than to the operation of a fluid, 

 which they thought was so obviously destitute of all 

 weight. It was accordingly considered as an indis- 

 putable fact, that the ascent of water in pumps, and 

 other similar effects of atmospherical pressure, were 

 owing to the horror which nature has for a vacuum. 

 This opinion was universally received till the 6uper- 

 intendant of the water works of the Grand Duke of 

 Tuscany, wishing to raise water, by means of a pump, 

 to a considerable height, was surprised to find that 

 the water would not rise higher than 32 or 33 feet. 

 After he had ascertained that this could not be ascri- 

 bed to any defect in the construction of the pump, he 

 mentioned the circumstance to Galileo, and requested 



him to give him an explanation of the cause of this Barometer- 

 anomaly. Galileo, either not questioning the just- v" -' 

 ness of the opinion which then prevailed, or being 

 unable to assign any other that was more plausible, 

 replied, " That the water was raised to the height of 

 32 feet on accpunt of the horror which nature has for 

 a vacuum ; but that the horror wis limited in its ef- 

 fects, and ceased to operate above the height of 32 

 feet !" This explanation, so unworthy of the name 

 of Galileo, would be totally undeserving of credit, did 

 we not know the authority that an error which has 

 prevailed fortwenty centuries could have over the hu- 

 man mind. It appears, however, that he was by no 

 means satisfied with the explanation which he had given, 

 and that he immediately began to suspect the agency 

 of some external cause ; but his death, which happen- 

 ed soon after, prevented him from bringing his thoughts 

 to maturity. His disciple Torricelli, to whom it is Experi- 

 supposed he had mentioned his ideas on the subject, mem of 

 was more successful in his explanation. He suspect- Torricelli. 

 ed that the weight of the water was one of the elements 

 which ought to be taken into consideration in inves- 

 tigating the cause of the ascent of that fluid in pumps, 

 and that it was probably counterbalanced by the 

 weight of something external pressing upon the sur- 

 face below. To put this conjecture to the test of 

 experiment, he took a glass tube about four feet long, 

 (as AB, Fig. 2.) hermetically sealed at one end A, Plat* 

 and open at the other. Having filled it with mercu- '.HI. Fig. '- 

 ry, he shut the open end with his finger ; he then 

 inverted the tube, and introduced the open end of it 

 under the surface of a small quantity of mercury in 

 a bason. Lastly, he placed the tube in a vertical 

 position, and on withdrawing his finger, he observed 

 that a part of the mercury descended in the tube, and 

 that the rest of it was supported at the height of 27 

 inches above the level of the mercury in the bason. 

 By varying the experiment, he found that, in all 

 cases, the mercury was supported at a perpendicular 

 height above its surface in the bason, equal to about 

 the 14th part of the height of the water in the pumps. 

 He therefore inferred, that the mercury in the tube, 

 and the water in the pump, exerted equal pressures on 

 the same base, their altitudes being inversely as their 

 specific gravities, and that the weight of the column 

 in either case was counteracted by some fixed and de- 

 terminate force. This force he supposed was the 

 weight of the air. 



This explanation, however natural and obvious it 

 may now seem, was by no means so readily admitted 

 as might have been expected from its extreme plausi- 



