148 Royal Society. 



The first three values being remarkably coincident, and the last dif- 

 fering from them by about -j^th of the whole. 



The air collected in the ascents was analysed by Dr. Miller ; he 

 states that " the specimens of air do not differ in any important 

 amount from that at the earth at the same time, but contain a trifle 

 less oxygen. All of them contained a trace of carbonic acid, but 

 the quantity was too small for accurate measurement upon the small 

 amount of air collected." 



June 9. — The following papers were read : — 



1 . " Further Experiments and Observations on the Properties of 

 Light." By Lord Brougham, F.R.S., Member of the Institute of 

 France. 



1 . The author considers that Sir Isaac Newton's experiments to 

 prove that the fringes formed by inflexion and bordering the sha- 

 dows of all bodies, are of different breadths when formed by the 

 homogeneous rays of different kinds, are the foundation of his theory, 

 and would be perfectly conclusive if the different rays were equally 

 bent out of their course by inflexion, for in that case the line joining 

 the centres of the fringes on opposite sides of the shadow being, as 

 he found them, of different lengths, the fringes must be of different 

 breadths. He found that line to be -^ inch in the red, j\ in the 

 violet of the nearest fringe ; T V in the red, -Jy in the violet of the 

 second fringe ; and these proportions he found to be the same at all 

 distances of the chart from the hair. But if the rays are of different 

 flexibility, if the red, for example, is bent to a greater distance from 

 its course than the violet, the experiment becomes wholly inconclu- 

 sive ; and the line joining the centres may be greater in the red than 

 in the violet, although the breadths of the two fringes are equal, 

 or even though the violet fringe may be broader than the red. 



2. A variety of experiments are adduced in the paper to show that 

 this property of different flexibility exists, which Sir I. Newton had 

 not remarked. These experiments are either made with two bodies 

 acting jointly on the rays, or with a single body so acting. 



3. When made with two bodies, as sharp edges, these edges 

 must be perfectly parallel, and when placed in the axis of the pris- 

 matic spectrum they form fringes more distant in the red than in 

 any other part ; least distant in the violet. The fringes are both 

 broadest in the least refrangible rays and most removed ; narrowest 

 and least removed in the most refrangible. They incline from the 

 red towards the violet. 



4. The same experiment is easily made with a lamp or candle, 

 placing a prism between the flame and the edges. This renders 

 that exact parallelism of the edges which is required in the experi- 

 ment with the spectrum, comparatively immaterial ; because a con- 

 siderable inclination of the edges, as at an angle of half a degree or 

 more, does not affect the action on the rays in the very small space 

 through which they pass by the edges. 



5. With a single edge, or other body as a hair, the same difference 

 in the position, as well as in the breadth of the fringes, is found to 

 be observable, though not so manifestly as when two act together on 



