CATAtOGUE. — MET EORO LOGY, II VGROMETERS, 



469 



Sflge on Ulcke's hygrometer. Roz. XXXIV. 



58. 

 Geoffrey on the hair hygrometer. Roz. 



XXXIV. 255. 



Attributes to it some irregularities. 



Volta on the use of the electrometer in hygro- 

 nietrv. Soc. Ifal. V. 551. 



Ascertaining the velocity of the dissipation of electricity. 



Leslie's hyjirometer. Nich. UI. 401. Gilb. V. 



23(5. X. no. 

 Leslie on moisture absorbed by earths and 



stones. Glib. XII. 114. 



Says, that rarefaction lessens the action considerably. 

 Heated flannel dries the air very effectually. 



Hofhheimer's hygrometer. Ph. M. 1.36?. 



Weighing a plate of glass, to which the moisture is sup- 

 posed to adhere. 

 Ludicke on hygrometers. Gilb. I. 282. II. 



70. V. 70. X. no. 



Mr. Ludicke considers the result of his experiments as 

 very favourable to Mr. Leslie's hygrometer. He proposes to 

 improve it, by employing two mercurial thermometers with 

 very fine tubes, fixed to the same support, and having their 

 bulbs very near together ; one of the tubes is to be curved; 

 and the bulb, being first blown larger than is necessary, is 

 to have a portion depressed, so as to form a dish for the re- 

 ception of water, which it will supply for many hours, 

 without the interruption occasioned by renewing it: the 

 eold produced by the evaporation is then considered as the 

 measure of the dryness of the air. It would however be 

 «asy to supply the quantity of water necessary, without giv- 

 ing the bulb a form so peculiar. The hair hygrometer ap- 

 peared, in the comparison, to indicate the maximum of 

 moisture too early. 



Voigl's hygrometer, of a quill cut spirally. 



Gilb. III. 126. 

 Quill hygrometer. Gilb. IV. 477. 

 Zylius on the hygrometer, and in answer to 



remarks. Gilb. V. 257. VIII. 342, 

 Remarks in answer to Zylius. Gilb. VI. 236. 

 - Forster's hygrometer. Ph. M. XI. I67. 



From the beard of the avena sterilis. 

 Dalton. Manch. M. V. 

 Parrot on hygrometry. Gilb. XIII. 244. 

 Bockmann's comparison of the hygrometers 



of Leslie, Saussure, and Deluc. Gilb. XV. 



355. 



The wind affects Leslie's hygrometer very materially : the 

 others do not agree well with each other. Deluc's seems to 

 be a Tittle less depressed by an elevation of temperature than 

 Saussure's. 



On the Indications of Hygrometers. 



Deluc observes, that when the grass is covered with dew, 

 the air above it is often far from the state of extreme mois- 

 ture, the hygrometer standing at 50" or 55" ; that extreme 

 moisture, as indicated by the hygrometer, seldom, but 

 sometimes, exists in the open transparent air; that at great 

 heights the air is very dry, excepting the clouds. The 

 mean moisture in London, as indicated by Deluc's hygro- 

 meter, is 79", or -,'5^ of the extreme moisture. The whole 

 expansion of the vv-halebone is about |. 



Deluc says, that substances immersed in alcohol and 

 ether were expanded almost as much as when immersed in 

 water. Ph. tr. 1791. Saussure found that no vapours except 

 that of- water affected his hygrometer. Hygrometrie. 



Deluc produces extreme dryness in a vessel accurately 

 closed, with hot lime in it ; extreme moisture by a wire cage 

 covered with cloth, having a reservoir at the top to keep it 

 moist, which is enclosed in a jar over water : here the 

 whalebone hygrometer rises slowly but certainly to 100°, 

 the hair falls to 98°. 



Slips of substances cut across the grain, preserve a march 

 more consistent with the increase of weight than threads. 

 Glass becomes wet when Deluc's hygrometer stands at 80°, 

 metals and other substances, at 100°. Cnventry's hygro- 

 meter, of paper weighed, is a very delicate test. 



According to Mr. Deluc, air in a vessel with water does 

 not attain the maximum of moisture, except in very low 

 temperatures ; the whalebone hyi^rometer usually standing 

 at 80", Saussure's at 100°. There is generally an atmo- 

 sphere of extreme moismre an inch or two above the surface 

 of the water in a close vessel, the glass becoming clouded 

 by the slightest change of temperature. 



Deluc found the expansion of a hair corresponding to the 

 degrees of his hygrometer thus : 



Bockmann found 10° of Deluc correspond to about 3S' 



