256 
LORD BROUGHAM’S EXPERIMENTS AND OBSERVATIONS 
edges are placed parallel to these two sides of the rays ; and thus the connection of 
the fringes in question, with the preceding action of which disposed and polarized, 
is clearly proved. 
4. It is an obvious extension and variation of this experiment both to apply edges 
parallel to the first and disposing edges, and also to apply edges at right angles to 
their direction; and important results follow from this experiment. But until a more 
minute examination of the phenomena with accurate admeasurements can be had, I 
prefer not entering on this subject further than to say, that the extreme difficulty of 
obtaining fringes or images at once from the edges parallel to the first two, and 
from edges at right angles to these, indicates an action not always at right angles to 
the bending body, but whether conical or not I have not hitherto been able to ascer- 
tain. That the first body only disposes and polarizes in one direction is certain. 
But it seems difficult to explain the effect of the first two edges in preventing the 
fringes or images from being made by the second at right angles to those formed by 
the first two edges, if no lateral action exists. One can suppose the approaching of 
those two first edges to make the fringes narrower and narrower than those which 
the second two edges form when placed at right angles to the first. But this is by 
no means all that happens. There is hardly any set of fringes at all formed at right 
angles to the first set (parallel to the first two edges) when the first two are ap- 
proached so near each other as greatly to distend the disc. 
5. I reserve for future inquiry also the opinion held by Sir I. Newton, that the 
different homogeneous rays are acted upon by bodies at different distances, this action 
extending furthest over the least refrangible rays. He inferred this from the greater 
breadth of the fringes in those rays. 
It is in my apprehension, though I once held a different opinion*, not impossible 
to account for the difference of the breadth of the fringes by the different flexibility 
of the rays ; and the reasoning in one of the foregoing propositions shows how this 
inquiry may be conducted. But one thing is certain, and probably Sir I. Newton 
had made the experiment and grounded his opinion upon the result. If you place a 
screen, with a narrow slit in the prismatic spectrum’s rays, parallel to the rectilinear 
sides, and then place a second prism at right angles to the first and between the 
screen and the chart, you will see the image of the slit drawn on one side, the violet 
being furthest drawn, the red least drawn ; but you will find no difference in the 
breadth of the image cast by the slit. Flexion, however, operates in a different man- 
ner, because it acts on rays, which, though of the same flexibility, are at different 
distances from the body. 
6. The internal fringes in the shadow (said by interference) deserve to be ex- 
amined much more minutely than they ever have been ; and I have made many ex- 
periments on these, by which an action of the rays on one another is, I think, suffi- 
ciently proved. I shall here content myself with only stating such results as bear on 
* Philosophical Transactions, 1797. 
