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Show [ 172 ] Taught with fweet fmiles, refponfive to their prayer, The fpring and preffure of the viewlefs air. -How up exhaufied tubes bright currents flow Ot liquid filver from the lake below, Weigh the long column of the incumbent fkics, And with the changeful mon1ent fall and rife: -How, as in brazen pumps the pifions move, The 1nen1brane-valve fufl:ains the weight above ; 135: by the expanfion of air. For a thermometer placed in the receiver finks fome degrees;. and in a very little time, as foon as a fufficient quantity of heat can be acquired from the furrounding bodies, the dew becomes again taken up. See additional notes, No. VII. Mr. Sauffu re obferved on placing his hygrometer in a receiver of an air-pump, that .though on beginning to exhaufl: it the air became mifl:y, and parted with i-ts moifl:ur:e, y.et the hair of his hygrometer contracted, and the infl:rument pointed to greater drynefs. This unexpected occurrence isex..pl ained by M. Monge (An nales de Chymie, Tom. V.) to depend on the want of the ufual preffure of the atmofphcre to force the aqueousparticles into the pores of the hair; anJ M. Sauffurc fuppoles, that his veficular vaoom: requires more time to be recllffolved, than is necefliuy to dry the hair of his thennom~ter. Effais fur l'Hygrom. p. '2.26. but I fufpeCl: there is a lefs hypothetical way of underfianding it~ when a colder b~d~ is br.ought into warm and moifl: air, (as a bottle of fpringwater for mllance,) a fl:eatjllS qutckly colleeted on its furface ; the contrary occurs when a warmer body is brol1ght into colu and damp air, it continues free from dew fo . long as it continues warm; for it warms the atmofphere around it, and renders it capable of receiving infl:cacl of parting with moifl:ure. The moment the air becomes rarefied in the receiver of the air-pump it becomes colder, as appears by the thermotneter and depofits its vapour; but th <; luir of Mr. S:mflure's hygrometer is now wanner tha~ the air in which it is im.mcrfed~ and i.n confeq:1ence becomes dryer than befo re, by \!arming the air which tmmc\.hatcly !urroumls lt, a part of its moifl.ure evaporating . along with its heat. [ 173 ] Stroke follows fl:roke, the gelid vapour falls,. And mifiy dew-drops dim the cryfial walls ; Rare and more rare expands the fluid thin, And Silence dwells with Vacancy within.So in the mighty Void with grim delight Primeval Silence reign' d with ancient Night. 2. "SYLPHS! your [oft voices, whifpering from the fkies., Bade from. low earth the bold MoNGULFIER rife ; Outfl:retch' d his buoyant ball with airy fpring, I 45 And bore the Sage on levity of wing;- Where were ye, SYLPHS! when on the ethereal main- Young RosrERE launch'd, and call'd your aid in vain?· Fair n1ounts the light balloon, by Zephyr driven, Parts the thin clouds,. and fails along the heaven ; I 5o Young Rofierc lrwnch'd. l. q.S. M. Pilatre du Rofiere with aM. ~om~in r?fe in a balloon from Boulogne in June 1785, and after having been about a m!le htgh f~r about 1\alf an hour the balloon took fire, and the two adventurers were dafhed to pteces on· their fall to the ground . Mr. Rofiere was a philofnpher of great talen s_an~ aCl::'it~·· joined with fw .. h urbanity and elegance of manners, as conciliated the aflcClJOn.~ ot htS · acquain!ance :wd rendered his misfortune univerfally lamcntell. Annual Regdtcr forr 1:784 antl q85, P· 329, |
