150 ANNUAL OF SCIENTIFIC DISCOVERY. 



polarized; nevertheless, without some observation we cannot discover its 

 cause. If the light be polarized in a plane passing through the sun, the 

 comet and the eye, we must infer that it is polarized by the reflection of the 

 light coming from the sun ; if it be polarized in an opposite plane, the polar- 

 ization may be due to the refraction of the atmosphere. If it be polarized 

 qua qua versus, this may be due to these causes, viz., to refraction by the sur- 

 faces of the object-glasses and eye-piece, to the imperfection in the annealing 

 of the glass of which the lenses are formed, or to the fact of one or more of the 

 lenses being pinched in their cell. Supposing it to be an effect of the first of 

 these causes, the opening of the object-glasses and eye-piece should be 

 reduced to a central band, which would eliminate the light polarized in an 

 opposite plane, and leave that which is polarized in a plane perpendicular to 

 the direction. By turning the telescope on the lenses, the direction of the 

 polarization would be changed. 



If the polarization be produced by a defect in the annealing of the glass 

 of which the lenses are made, the existence of this imperfection will be ren- 

 dered evident by exposing the lenses to polarized light. 



If the polarization observed be due to the reflection of the rays of the sun 

 by the comet, or its envelope, small stars will be seen more distinctly when 

 the polarized light is extinguished by the application of a Xicol's prism. 



Objects rendered visible in a fog. Whilst I was studying the polarization of 

 the atmosphere, I observed this remarkable fact, that when distant objects are 

 rendered indistinct by the interposition of a light fog, a part of their definite- 

 ness may be restored by looking at them through a Nicol-prism, Avhich stops 

 all the light which the fog has polarized in a plane passing through the sun, 

 the object, and the eye of the observer. The objects thus made more dis- 

 tinct and visible, were seen through that portion of the fog in which the . 

 polarization of the reflected light was at a maximum. This method of ren- 

 dering visible, objects rendered indistinct by fogs, may, it appears to me, 

 receive important applications in military and naval operations. 



OX THE FOR31 OF THE EYEBALL, AND THE RELATIVE POSITION OF 

 THE ENTRANCE OF THE OPTIC NERVE INTO IT IN DIFFERENT 

 ANIMALS. 



In a paper on the above subject presented to the British Association, 18o8, 

 by Mr. T. Xunneley, the author observed that the orbits of the eyes are much 

 larger than the eyeballs, and that their axes diverge considerably in an out- 

 Avard direction, Avhile those of the two eyes are perfectly parallel. The eye- 

 balls lie in the fore-part of the orbits, and according as they are more or less 

 prominent, and more or less covered Arith the lids, do they appear to be larger 

 or smaller. The eye of the infant is larger, in proportion to the size of the 

 bod}', than that of the adult; but it is by no means certain that the eye of the 

 male is larger proportionately to the size of the body than the eye of the 

 female. By some anatomists the human eye Avas described as a spheroid, 

 the diameter of which, from before to behind, is greater than in any other 

 direction. He had measured a great number" of eyes, of the human subject 

 as Avell as of animals, and he found that Avherever there was a departure 

 from the spherical figure, it Avas in the direction contrary to that Avhich had 

 been commonly stated. In some instances the difference betAveen the two 

 diameters Avas scarcely perceptible; in all, Avhere a distinction was observed, 

 the transA-erse Avas the greatest. He had prepared a set of tables (Avhich were 



