.is blown out the hmp finks , to the tottom ; and even a lamp with its bafe 



thin .lamina of talc feifs very welf'tiMthe flame iS extineuifhed, and then it ii 



> ,.i '•'"'•••,'■■ 'I.-- - ■f.-'. ! -Jifif . .., .-^Ii n.,,7' "^ 1'....,... , 

 link'. .• ..-.;,.,, 



170 ^ccoitni of a Jilf-iiiowig Lamp, 



1- ■'-'■• -I ' ' ■ -^ '. J' •.:.. . ■ .'t ,T.. 



of the. bafe neareft the wick, and aid tj^e re-aifilion.of the recoiling dream, by making ttj9 



lamp. fail. in the oppofite direilion, as it were down hill. 



That the rarefied oil linden the bafe has really a conflarit tendency to rife above the ge- 

 neral level, feems undeniable from the following faflsV namely, that 'after any of the lamps 

 has burned a little while, and. has got its bafe foaked witb the oil, as foon as the flame 



made of a 

 immediately 



• Agreeable to tne explanation" .wfiichnas now i)efett 'ak6mpted,'r found that when a to- 

 pical heat was applied to the iurface of the oil, by bi'inging the point of a poker dully red 

 hot nearly into contact, there was foon produced a fuperficial ftream or efflux from the iron 

 in all directions, .which cleared the face of the oil from the charcoal duft in a wider and a 

 Wider circle, tillat'Uft the whole particles were crowded together at the confines of the 



bafon. 'V . J. , , I,, 



When the oil in' 'tfifs 'experiment was (baltow; having goM leaf beat into very minute- 

 parts mixed with it, an oppofite flream was obferved below fetting in towards the poker in 

 all directions, and then rifing upwards. But this general tendency of all the parts of the 

 fluid, of moving in (^uefl of an equilibrium, is illuflrated in a very entertaining manner as 

 follows : Into a tea cup or punch gL.fs nearly filled with pure water, pour a deflcrt fpoonful 

 ofvery.clear fallad oil with.minute particles dfgold leaf in it. If the water be cold, the oil 

 when poured on at the tenfrc, leifurely and cbntinuedly, will reft upon the furface in the 

 form of a lens, and remain infulated' and eq'uidiftant from' the fides of the veflel. A 

 little lamp, when put upon this lens of , oil and lighted, will fail and circulate as long?r 

 ones do in a bafon. If it be rK)W madfe to ftand flill, it is very amufing to obferve the mi- 

 nute particles of the gold perpetually thrown out brifkly at the ftern in the fuperficial cur- 

 rent, whilil the particles' in the fund of the lens creep in all dire<£lions towards the lamp, 

 and at laft rife up ufidfei-'tnebafe towards the flame, as the great centre of attraction, till 

 they are caught by the retreating fuperficial ftream, in which they rapidly trend ofFto fome 

 diHance, when again they fink to renew the circulation. 



When a patch of paper, or a wafer, or fuch light body, fwims upon the oil in the bafon, 

 the point of a hot iron held near to it makes it flit its place, and move away by a feeming 

 repulfion ; but in reality by the heat generatinga fuperficial ftream flowing from the iron in 



■ all direaionsi'"' '^ '^"'■!', ^^^ "'."* ^" =''^' ' ">' -•'o^- 



' Again,if upon oil of tOrperrtine, £Ether, alcohol, or any of the inflammable fluids polTeif- 

 ing much tenuity, you throw a wafer much heated, it will immediately glide away and con- 

 tinue in m'otlon till it cools ; when the ftream which ifliied from fome part' of it moft co- 

 'pioufly teafeS'." DbiibleVti'ni^Tnelted tallow,- bees- wax, and rofin, alfo afford the fiime con- 

 ' tinued efflu5^ at th6 hrtAce upon a topical application of.beat, and the fame phenomena as 

 the oil does when little lamps are made to fwim in them. It is fomewhat remarkable, 

 'however, that though the inflammable fluids all agree in this, yet the topical application of 



■ heat at the furface of water does not produce fimilar effedts. 



For, if the point of a poker neaily red hot be held very clofc to the furface of water in a 

 bafon, the particles of the charcoal diift do not at all glide away, as they do in the cafe of oil, 

 biit feem to acquire only a 'fldw irregular circular motion, which in time fpreads wider, 



■ • whilft 



