Physics. 267 
nardo da Newton conceived the color to be due to exceed- 
ingly small water particles acting as thin plates. Goethe’s experi- 
ments In connexion with this subject are well wn and excee 
connection with his truly beautiful experiments on the photograph- 
le power of sky-light, has also given various instances of the pro- 
: ization, moreover, was perfect. 
his experiments on fluorescence, Professor Stokes had contin- 
he n 
the iluorescent light of the same liquids, which he ascri 
true dispersion.” In fact it is hardly possibly to obtain a liquid 
which polarize by reflection the light falling upon 
spersed light being unpolarized. At p. 530 of his 
celebrated memoir “On the Change of the Refrangibility of 
a blue which was exceedingly like an 
eect of fluorescence, but which, when properly examined, was 
found to be an instance of false dispersion. “ It often struck me, 
i o 
* Thave sometimes quenched almost completely, by a Nicol, the light dis- 
charged normally from burning leaves in Hyde Park. The blue smoke from the 
‘gnited end of a cigar polarizes also, but not perfectly. 
Ni he azure may be produced in the midst of a field of motes. By turning the 
icol, the interstitial blue may be completely quenched, the shining, and appa- 
rently unaffected motes, remaining masters of the field. A blue cloud, moreover, 
: be precipitated in the midst of the azure. An aqueous cloud thus precipi- 
ated reverses the polarization; but on the melting away of the cloud the azure 
and its polarization remain behind. 
