VOL. LIV.3 PHILOSOPHIC AX TRANSACTIONS. 151 



XLf^I. The Description of a New Hygrometer. Invented by James Ferguson, 



F. R. S. p. 259. 



This machine is a frame of wainscot or mahogany, grooved in the innermost 

 edges of the two longest sides, for holding a pannel of white deal board, without 

 pinching it. The pannel is about the thickness of a crown-piece, and 15 inches 

 in length, crosswise to the grain of the wood. The middle part projects outward 

 from the upper and lower edges, where it is fastened into the frame by 2 screws, 

 to keep the middle part always in the same place, while the rest of the pannel 

 expands by moist air toward both ends of the frame, and contracts toward the 

 middle when the air is dry. 



In 3 or 4 years at most, a new pannel should be put into the frame ; because, 

 when the old one has been so long exposed to the air, it will almost cease to be 

 affected by it. And therefore, a large thick piece of deal should be kept in re- 

 serve for that purpose; and about the thickness of a card always planed off that 

 side from which the new pannel is to be taken. 



XLVII. Experiments and Observations on the Compressibility of Water and 

 some other Fluids. By John Canton, M. A., F. R. S. p. 26 1. 



In a paper lately laid before the r. s., Philos. Trans, vol. 52, p. 640, Mr. C. 

 not only related the experiments by which he found water to be compressible, 

 but also those by which he discovered how much a given weight would compress 

 it when in a temperate degree of heat. By similar experiments made since, it 

 appears that water has the remarkable property of being more compressible in 

 winter than in summer; which is contrary to what he had observed both in spirit 

 of wine and oil of olives: these fluids are (as one would expect water to be) more 

 compressible when expanded by heat, and less so when contracted by cold. 

 Water and spirit of wine he several times examined, both by the air-pump and 

 condenser, in opposite seasons of the year: and, when Fahrenheit's thermometer 

 has been at 34°, he has found the water to be compressed by the mean weight 

 of the atmosphere 49 parts in a million of its whole bulk, and the spirit of wine 

 60 parts; but when the thermometer has been at 64°, the same weight would 

 compress the water no more than 44 parts in a million, and the spirit of wine no 

 less than 7 1 of the same parts. In making these experiments, the glass ball 

 containing the fluid to be compressed must be kept under water, that its heat 

 may not be altered during the operation. 



The compression by the weight of the atmosphere, and the specific gravity of 

 each of the following fluids, which are all that he had tried, were found when 

 the barometer was at 294- inches, and the thermometer at 50°. 



