VOL. XIV.] PHILOSOPHICAL TRANSACTIONS. 16 



the narrower glass, to near 19 grains, gained in the broader; so that the time 

 of increasing bears, as near as can be expected, an exact proportion to the sur- 

 face of the hquor exposed, and the Hquor in the smaller glass having but ^ part 

 of the surface of the greater, could not be saturated under 9 times as many days 

 as the greater. 



The only use of it I can at present find will be to estimate moisture and dry- 

 ness in the air, which is evidently suggested by this following observation : that 

 when the oil of vitriol is saturated in the moistest weather, it afterward retains 

 or loses its acquired weight, as the air proves more or less moist. Thus, the 

 one grain above-mentioned, after its full increase, often varied its equilibrium, 

 viz. in dry weather; the weights, in moist, the liquor constantly preponderated, 

 and that so sensibly, that the tongue of the balance, of I-l inch long, described 

 an arch of variation to 4- of an inch compass, even with that little quantity of 

 liquor; so that if more liquor expanded under a large surface be used, the 

 minutest alteration of weather must needs much more affect it, and a bare 

 pair of scales will afford a hygroscope as nice perhaps as any yet known. — ^This 

 balance may be contrived in two ways; either such that the pin should be in the 

 middle of the beam, with a very slender tapering tongue, of a foot, or a foot 

 and half long, pointing to the divisions on a broad arched plate fixed above ; or 

 else the scale with the liquor may be hung to a point of the beam very near the 

 pin, and the other extreme made so long as to mark a large arch on a board, 

 placed conveniently for that purpose. The scale in either may be a concave glass 

 of 4 or 3 inches diameter. Lastly, on the division of the arches should be in- 

 scribed the different temperature of the air shown by the liquor. And it is pro- 

 bable that oil of sulphur per campanam, as also oil of tartar per deliquium, and 

 the liquor of fixed nitre, &c. may succeed as well as the oil of vitriol.* 



A hygroscope might also be made of a viol-string running over pulleys, and 

 suspending a bullet, connected to the shorter end of an index, the other ex- 

 tremity being so long as to describe a long arch, by the rising and falling of the 

 bullet, by the shrinking and stretching of the string; and this would be still 

 more nice, by fastening the index to the centre of the last pulley. 



Ricreatione deW Occhio e della Mente nelV Osservation' delle Chiocciole dal P. 

 Filippo Buonanni, &c. in Roma, per il Farese, 168I. N° 156, p. 507. 



A work on testacea or shell fish, which the author divides into univalves, 



* There is much ingenuity in this author's application of the property which oU of vitriol or con- 

 centrated sulphuric acid possesses of attracting moisture from the air, to hygrometrical purposes. 

 This mode, however, of measuring the varying humidity of the atmosphere, is superseded by the 



