EMISSION THEORY. 235 
of that of light; if the weight of a luminous molecule 
were the 640,000th part of that of the cannon ball, it 
would in like manner overthrow a wall. 
These deductions are certain: but let us look at the 
facts. A luminous molecule not only cannot overthrow a 
wall, but it even penetrates into an organ so delicate as 
the eye without occasioning the least pain, without even 
producing any sensible dynamic effect. We can say 
more: in experiments undertaken with the view of ren- 
dering sensible the impulsions of light, physicists have 
not been content to use an isolated agent, they have 
brought to act simultaneously the immense quantity of 
light which can be condensed at the focus of a large lens ; 
they have not opposed to the shock of the rays very re- 
sisting objects, but bodies so delicately suspended that a 
breath could derange them enormously ; they have ope- 
rated for example, on the extremity of a very light lever 
suspended horizontally by a spider’s thread. ‘The sole 
obstacle to the rotatory movement of such an apparatus 
would be the force of reaction, which the thread would 
acquire in twisting. But this force might be consid- 
ered as nothing, since from its nature it always increases 
rapidly with the degree of torsion ; and, in this instance, 
one of the observers whose experiments I am analyzing, 
found no perceptible force of this kind, after having had 
the patience to give the thread 14,000 turns, by turning 
the lever round on its centre. It is then well established 
that, in spite of their excessive velocity, myriads of lumi- 
nous rays acting simultaneously produce no perceptible 
force. But we should be going beyond the legitimate 
consequences which this interesting experiment author- 
izes, if we concluded that a ray is not composed of mate- 
rial elements endowed with a rapid motion of translation. 
