Dr. Young’s Lecture on 
28 
admitted, “ densius est, quam in spatiis hinc inde, dilatabit sese 
<c tam versus spatia utrinque sita, quam versus pulsuum rariora 
“ intervalla; eoque pacto — pulsus eadem fere celeritate sese in 
“medii partes quiescentes hinc inde relaxare debent; — ideoque 
“ spatium totum occupabunt. — Hoc experimur in sonis.” (Prill- 
cip. Lib. II. Prop. 42. 
“ Are not all hypotheses erroneous, in which light is supposed 
“ to consist in pression or motion, propagated through a fluid 
“ medium ?— If it consisted in pression or motion, propagated 
“ either in an instant, or in time, it would bend into the shadow. 
“ For pression or motion cannot be propagated in a fluid in 
“ right lines beyond an obstacle which stops part of the motion, 
“ but will bend and spread every way into the quiescent medium 
“ which lies beyond the obstacle. — The waves on the surface of 
“ stagnating water, passing by the sides of a broad obstacle 
“ which stops part of them, bend afterwards, and dilate them- 
“ selves gradually into the quiet water behind the obstacle. 
“ The waves, pulses, or vibrations of the air, wherein sounds 
“ consist, bend manifestly, though not so much as the waves 
<f of water. For a bell or a cannon may be heard beyond a 
“ hill, which intercepts the sight of the sounding body; and 
« sounds are propagated as readily through crooked pipes as 
“ straight ones. But light is never known to follow crooked 
“ passages, nor to bend into the shadow. For the fixed stars, 
“ by the interposition of any of the planets, cease to be seen. 
“ And so do the parts of the sun, by the interposition of the 
Ci moon, Mercury, or Venus. • The rays which pass very near 
« to the edges of any body, are bent a little by the action of the 
« body but this bending is not towards but from the shadow. 
