PHYSICAL AND LITERARY. 6f 



municated to the whole water in the former 

 cafe than in the latter. There is this advan- 

 tage too in ufing a plain furface of foap-wa- 

 ter, that, before it freezes, the obferver 

 may draw out any particular colour or feries 

 of colours, which he chufes, to a greater 

 breadth, by ftroaking it along with a wet 

 finger. For this reafon, amongft others, 

 I have found it a more convenient fubjedt for 

 examining the various orders of colours, than 

 fpherical bubbles adhering to a plane. Per- 

 haps, melted rofin might be drawn out into 

 a thin-coloured plate before it hardens j for 

 I have often blown it into bubbles with a to- 

 bacco-pipe till it became coloured. I know no 

 other ways in which the various orders of co- 

 Jours can bepreferved for deliberate infpedion, 

 but either in a frozen plate of water or rofin, 

 or in the permanent J'coria that appear on 

 heated metals. I have counted, on the fide 

 of a clean-polifned copper tea-kettle, the 

 fix firft orders of colours diftiniflly and regu- 

 larly ranged in the fame fucceflion in which 

 they appear in the foap-bubbles ; the firft or- 

 der being formed on that part of the kettle 

 that had been leaft heated. 



QUER, 



