246 
LORD brougham’s EXPERIMENTS AND OBSERVATIONS 
sisted of two plates, A and B (Plate VL), with sharp rectilinear edges, one, A, hori- 
zontal, the other, B, moving vertically on a pivot, and both nicely graduated. The 
angle at which the second plate was vertically inclined to the first, was likewise ascer- 
tained by a vertical graduated quadrant E. Moreover the edges moved also hori- 
zontally, and their angle with each other was measured by a horizontal graduated 
quadrant K. There was a fine micrometer F to ascertain the distances of the two 
edges from each other, and another to measure the breadth of the fringes on the 
chart. The observations made with this instrument gave me undoubted assurance 
that the equation to the curve M N in fig. 11 \syx-=a, a conic hyperbola, and that 
the disposing force is inversely as the distance at which the flexion of the rays bent 
and disposed takes place. 
Scholium . — It is rlear that the extraordinary property we have now been examining, 
has no connexion with the different breadths of the pencils at different distances 
from the point of the first flexion, owing to the divergence caused by that flexion. 
By the same kind of analysis, which we shall use in demonstrating the 6th Propo- 
sition, it may be shown,— that the divergence of the rays alone would give a 
different result, the fringes made by an inffexion following a deflexion and those 
made by a deflexion following an inflexion ; secondly, that in no case would the 
equation to the disposing force be the conic hyperbola, even where that fringe de- 
creased with the increase of the distance ; thirdly, even where the effect of increasing 
the distance is such as the dispersion would lead to expect, the rate of decrease of 
the fringes is very much greater in fact than that calculation would lead to, five or 
six times as great in many cases ; and lastly, that instead of the law of decrease being 
uniform, it would, if caused by the dispersion, vary at different distances from the two 
edges*. Nothing therefore can be more manifest than that the phenomena in ques- 
tion depend upon a peculiar property of the rays, which makes them change in their 
disposition with the length of the space through which they have travelled. 
It should seem that light may be compared, when bent and thereby disposed, to a 
body in its nascent state, which, as we find by constant experience, has properties 
different from those which it has afterwards ; and I have therefore contrived some 
experiments for the purpose of ascertaining whether or not light at the moment of 
its production (by artificial means) has properties other than those which it possesses 
after it has been some time produced. This will form the subject of a future inquiry. 
I would suggest, however, at present that the eleetric fluid ought to be examined with 
a view to find whether or not it has any property analogous to disposition, that is, 
whether it becomes more difficultly attracted at some distance from its evolution, as 
light is more difficultly bent at a distance from the point of its being disposed. On 
heat a like experiment may be made. The thermometer would no doubt stand at a 
different height at different distances from the source of the heat ; but the question 
* I have given demonstrations of these propositions in a memoir presented to the National Institute, but I 
am reluctant to load the present paper with them. 
