498 
POPULAR SCIENCE REVIEW. 
Mr. Field, in a satisfactory manner, to be in the numerical 
proportional power as follows : — yellow, three ; red, five ; and 
blue, eight. When these three colours are reflected from any 
opaque body in these proportions, white is produced ; they 
are then said to be in an active state, but each is neutralized 
by the relative effect that the others have upon it. WTien they 
are absorbed, they are in a passive state, and black is the 
result. WTien transmitted through any transparent body, the 
effect is the same ; but in the first case they are material or 
inherent, and in the second impalpable or transient. Colour 
therefore depends entirely on the reflective or refractive power 
of bodies, as the transmission or reflexion of sound does upon 
their vibratory powers. By the nndulatory theory of light, 
philosophers account for the variously coloured rays of the 
solar spectrum, by calculating the differences in the frequency 
of the vibrations of each ray — that is, the rays of light are 
supposed capable of vibrating in waves of different lengths. 
The shortest waves produce violet light, the longest red ; and 
with such precision have some of the more complex phenomena 
of light been studied, that mathematicians have absolutely been 
able to calculate the number of vibrations necessary to produce 
an impression of either white or coloured light. For instance, 
the periodical movements of the medium in white light regu- 
larly recur at equal intervals, five hundred millions of millions 
of times in a second of time ; in the sensation of redness, our 
eyes are affected four hundred and eighty-two millions of 
millions of times ; of yellowness, five hundred and forty-two 
millions of millions ; of violet, seven hundred and seven 
millions of millions ; and so on. 
How seldom do the most reflecting amongst us think, as we 
gaze on the flowers composing a bouquet, and inhale their 
fragrance which perfumes the surrounding air, that in order 
to distinguish the yellow tint of the laburnum, five hundred 
and forty-two millions of millions of undulations of light must 
occur ; that the ruby fuschia requires the eyes to receive four 
hundred and eighty-two millions of millions of undulations in 
a second ; that the violet’s tint is only distinguishable when 
seven hundred and seven millions of millions of vibrations 
have penetrated to the sensitive retina ! 
When objects are illuminated by homogeneous yellow light, 
the only thing which can be distinguished by the eye is the 
difference of intensity or brightness. It is now a generally 
received opinion that different bodies, according to the manner 
in which their minutest particles are arranged, possess the 
power of variously absorbing- a part and reflecting the other 
portionof the rays of light that fall upon them; and that on 
the proportions of the rays absorbed and reflected does the 
