small heavy Bodies in Air, &c. 257 



When water is dissolved in air, it constitutes, together with 

 it, a fluid perfectly transparent, all refractive power of the 

 water, whatever it may be, upon whatever it may depend, 

 ceasing. When separated from this state of solution, by the 

 aggregation, from whatever cause, of the dissolved particles, 

 their first action upon light passing through them, are of inflec- 

 tion by the air in which they float adjacent to each. By fur- 

 ther accession of particles, globules are constituted, through 

 which the light passes, and in passing in and out, is subject to 

 the ordinary reflections and refractions of transparent bodies, 

 by refractive powers, beginning at smaller sizes, and increasing 

 as those increase, up to the ordinary refractive power of large 

 masses of water in air. This gradual acquirement and increase 

 of refractive powers obviously follows from the phaenomena of 

 thin plates of water in air, or of air between glass. In the case 

 of a bubble of water in air, when the tenuity of the film at the 

 top is extreme, it ceases altogether to act in that part on the 

 light, which passes through, as if no body was interposed be- 

 tween the parts of air ; at increasing distances from the top, the 

 tenuity of the film increases, but not sufficiently to possess any 

 refractive or reflective powers ; the light arriving in the water 

 between the parts of air adjacent to the water, is inflected by 

 the air into two portions, one of which passes on, the other 

 returns ; and these inflections are continued and varied in 

 orders, dimensions, and colours, until at last at increased dis- 

 tances and adequate thicknesses they cease, and the ordinary 

 reflections and refractions are restored to the water at both 

 surfaces of the film. As this is effected, gradatim not per 

 aaltum, these powers beginning and increasing pass through 

 difterent states of intensity, from evanescence to their ordinary 

 state. The same is the case of air between two plates of glass, 

 and the evanescence, restoration, and gradual increase of the 

 refractive powers of transparent fluids, in these and similar cir- 

 cumstances, is thus fairly established, together with every prin- 

 ciple necessary to the formation of this iris. 



These globules may occawionully be so formed and ar- 

 ranged into sUise of various directions, as at once 



