When fwimming in a B A S 1<[ of OIL, &c. 169 



Again, if upon oil of turpentine, sether, alcohol, or any of 

 the inflammable fluids pofTefllng much tenuity, you throw a 

 wafer much heated, it will immediately glide away, and con- 

 tinue in motion till it cools ; when the ftream, which iflued 

 ► from fome part of it moft copioufly, ceafes. Double rum, melt- 

 ed tallow, bees wax, and rofin, alfo affbrd the fame continued 

 efflux at the furface, upon a topical application of heat, 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 fi- 

 milar eff'edls. 



For if the point of a poker nearly red hot be held very 

 clofe to the furface of water in a bafon, the particles of the 

 charcoal dull do not at all glide away as they do in the cafe of 

 oil, but feem to acquire only a flow irregular circular motion, 

 which in time fpreads wider, whilft the floating motes or particles 

 of dufl: keep nearly their relative places ; and the fame thing hap* 

 pens, though the point of the iron touches the water, fo as to 

 make it fimmer. 



I DO not well know how to account for this, unlefs it may be 

 a confequence of the known much lefs expanfibility of water 

 by heat, compared to that of the inflammable fluids, and which 

 may be fo inconfiderable as not to deftroy the equilibrium, fo 

 far as to produce an efllux from the lighter and expanded fluid 

 immediately under the heated body. Poflibly, too, the parts 

 of the water, as foon as heated, may tranfmit the furplus tempe- 

 rature to the contiguous colder water much more rapidly than 

 the inflammable fluids do in like circumftances, and thereby re- 

 fifl; the high temperature, neceflary to that degree of expan- 

 fion, which would difl;urb the equilibrium, and produce an ef- 

 flux ; not to m.ention that the maximum of this temperature 

 can never, at any rate, exceed 212", the boiling point of water. 



Vol. IV. X That 



