caused by atmospherical Refraction. 243 



object, the progress of the visual rays, (or axes of the pencils 

 received by thi eye,) it will be manifest that, 



Any object seen through the inclined concave part rm, Fig. 5. 

 would appear elevated, erect, and somewhat diminished. 



An object seen through md, where it is convex and inclined, 

 would be elevated ; and, if situated beyond the focus of visual 

 rays from the eye, it would appear inverted. The magnitude 

 would depend on the relative distances of the eye and object. 



Below the point d, where the curve terminates, vision would 

 be direct, so that an object might be situated so as to be seen in 

 all three ways at the same time, direct at O, inverted at I, and 

 erect again at A. 



I consider the foregoing propositions as applicable to all cases 

 of varying density, whether occasioned by mutual solution of 

 different fluids, or partial rarefaction of the same fluid; and, by 

 trial of various fluids, however different in density, or even in 

 viscidity, I find that the refractions observe a law agreeable to 

 the theory, as will appearby the following experiments. 



Experiment 1. Into a square phial containing a small quan- 

 tity of clear syrup, I put about an equal quantity of water, in 

 such a way that it floated on the surface of the syrup, without 

 mixing. For a short time, the stratum of union was so thin 

 that nothing could be distinctly seen through it. But soon, by 

 mutual penetration of the water and the syrup, the effects 

 represented at A, Fig. 6, were produced. 



Through the syrup, a word written on a card placed behind 

 was seen erect, and in its place ; through the adjacent variable 

 medium, an inverted image was visible above the true place; 

 and also, above that, a second image of the same object appeared 

 erect. 



