and its Occurrence in Lubrication. 35 



"Obs. 11. When the Water was between the Glaffes, if I 

 preffed the upper Glafs varioufly at its edges to make the Rings 

 move nimbly from one place to another, a little white Spot would 

 immediately follow the center of them, which upon creeping in of 

 the ambient Water into that place would prefently vanifh. Its 

 appearance was fuch as interjacent Air would have caufed, and 

 it exhibited the fame Colours. But it was not Air, for where any 

 Bubbles of Air were in the Water they would not vanifh. The 

 Reflexion muft have rather been caufed by a fubtiler Medium, 

 which could recede through the Glaffes at the creeping in of the 

 Water."] 



3—2 



