NATURAL PHILOSOPHY. 151 



eighth, and of human red blood-corpuscles magnified 400 diameters 

 by a Powell and Lealand's one-sixteenth immersion objective. 



COLOR-BLINDNESS. 



Mr. Monck, of Trinity College, Dublin, propounds a new and 

 interesting theory of color-blindness. The ordinary explanation 

 is, that the eye is not sensitive to certain colors, to which it is 

 objected that a color-blind person sees the whole spectrum, and 

 that were this explanation true, there should not be color-blind- 

 ness to complementary colors, red and green for example. Mr. 

 M. bases his theory on the phenomena of accidental colors. If 

 the eye be very sensitive to the excitation of the complementary 

 tint, then this latter, appearing with vividness while we are gaz- 

 ing upon the original color, is so combined with it as to give rise 

 to the grayish tint with which color-blind persons so often con- 

 found colors. The brighter the light, the more quickly and viv- 

 idly would the accidental color be produced, which explains the 

 fact that so many Daltonians see better in twilight. Another 

 argument is, that color-blind persons rarely see accidental colors. 

 According to this theory, then, the color-blind eye is one in 

 which the complementary color is seen very rapidly and very 

 vividly while looking at the primary color. If this view be cor- 

 rect the Daltoniaii will gain the best idea of a color by a tran- 

 sient glance at it, and in faint light. 



OPTICAL PROPERTIES OF BENZILE. 



A paper was read before the Academy of Science (Paris), by 

 M. Des Cloiseanx, " On the Optical Properties of Benzile and of 

 some Bodies of the Camphor Family, in the Crystallized State, 

 and in Solution." The author found that crystals of bcnzile 

 rotate the plane of crystallization in different ways, and the right 

 and left crystals, when dissolved and crystallized two or three 

 times, likewise give a mixture of crystals with opposite rotations. 

 Solution of benzile in ether has no action or polarized light. 

 Camphor of patchouli and mint camphor (menthole), both be- 

 longing to the hexagonal system, have a negative, uniaxial double 

 refraction, and their solutions in alcohol deviate the plane of 

 polarization to the left. Three camphors belonging to the cubic 

 system, namely, Bornean camphor, terecamphine, and mono- 

 hydrochlorate of turpentine, have no action on polarized light 

 when crystallized, but in solution strongly deviate the plane of 

 polarization to the right, the other two to the left. 



FIZEAU'S EXPERIMENTS ON " NEWTON'S RINGS." 



A comparison of the values of the wave-lengths of the light of 

 the two principal components of the D line of the solar spectrum, as 



