276 Mr Stevenson’s Lzperiments on Lights in Rapid Motion 
this effect was by no means so striking as the decrease of 
volume. 
3. Continuity of impression was not attained at the rate of 
5 flashes in a second, but each flash appeared to be distinctly 
separated by an interval of darkness; and even when the 
nearest approach to continuity was made, by the recurrence 
of 8 or 10 flashes in a second, the light still presented a 
twinkling appearance, which was well contrasted with the 
steady and unchanging effect of the cylindric refractor. 
4. The light of the cylindric refractor was, as already stated, 
steady and unchanging, and of much larger volume than the 
rapidly revolving flashes. It did not, however, appear so bril- 
liant as the flashes of the quickly revolving lenses, more espe- 
cially at the lower rate of 5 flashes in a second. 
5. When viewed through a telescope, the difference of yo- 
lume between the light of the cylindric refractor and that 
produced by the lenses at their greatest velocity was very 
striking. The former presented a large diffuse object of in- 
ferior brilliancy, while the latter exhibited a sharp pin point 
of brilliant light. 
Upon a careful consideration of these facts it appears war- 
rantable to draw the following general conclusions :— 
1. That our expectations as to the effects of light, when 
distributed according to the law of its natural horizontal di- 
vergence, are supported by observed facts as to the visibility 
of such lights, contrasted with those whose continuity of effect 
is produced by collecting the whole light into bright pencils, 
and causing them to revolve with great velocity. 
2. It appears that this deficiency of visibility seems to be 
chiefly due to a want of volume in the luminous object, and 
also, although in a less degree, to a loss of intensity, both of 
which defects appear to increase in proportion as the motion 
of the luminous object is accelerated. 
3. That this deficiency of volume is the most remarkable 
optical phenomenon connected with the rapid motion of lumi- 
nous bodies, and that it appears to be directly proportional to 
the yelocity of their passage over the eye. 
4, That there is reason to suspect that the visibility of dis- 
