THE APPLICATION OF SPECTRAL ANALYSIS TO PHARMACY. 
133 
analysis in chemistry, mineralogy, and astronomy. So much has been said and 
done lately by scientific observers in this direction, that one’s attention is na¬ 
turally attracted to other materials more intimately connected with every-day 
life. 
It is therefore with the hope of suggesting a practical use of spectral' analysis 
to your notice in a more immediate relation to our own profession, that I ven¬ 
ture to introduce my present subject. I do so with diffidence, because I have 
as yet only just passed the threshold of experiment, but have already seen 
enough to indicate that a large field of inquiry and interest lies before us. I 
hope therefore these few remarks may prompt some one present to work out the 
numerous details necessary for a more complete elucidation of the subject. 
Perhaps at the outset the question may arise, “What is spectral analysis?” 
I will, therefore, ask my more experienced brethren to bear with me while I 
give a short explanation before describing the method of working and showing 
some of its results. 
Works on the subject are nearly all filled with the phenomena of the spectra 
of flames. In the beautiful work of Professor Roscoe just published, this is the 
case ; only seven pages are devoted to what is commonly called “ the absorption 
spectrum.” 
You will all remember that Sir I. Newton, by passing a ray of light through 
a circular opening and then through a glass prism, showed what has been known 
ever since as “the solar spectrum,” the several rays being separated in the order 
of their refrangibility. 
Light may be regarded as an ethereal medium in an intense state of vibration, 
varying in rapidity from 470 to 800 millions of millions per second. The waves 
of light, too, as might be expected, vary in size proportionably to the rate of 
vibration. For instance, a ray of light that gives to the eye an idea of red 
vibrates, at the rate of 477 millions of millions in every second of time, each 
wave measuring about the an inch. When the rate of vibration reaches 
622 millions of millions, the wave measures only the an i nc K aQ d then 
produces the impression on the retina which we term blue. If the vibration 
exceeds 727 millions of millions, the eye cannot respond, and unless we use cer¬ 
tain precaution, there is no visible colour produced. The vibrations, neverthe¬ 
less, are there, because the chemical or actinic power is most intense. 
Colour, then, is not a substance per se , but is a certain, impression produced 
upon the retina, varying according to the intensity of vibration. 
The red rays of the spectrum vibrate so weakly that they can only penetrate 
the thin end of the prism. Those of greater intensity are capable of penetrating 
the thicker portions of the glass, and are thereby refracted at a greater angle. 
It was formerly thought that the three primary and pure colours of the spec¬ 
trum were red, yellow, and blue, and that neither of these could be further 
resolved, the intermediate tints being formed by the commixture of different 
waves of light. 
Later discoveries, however, of Professor Maxwell, Helmholtz, and Sir John 
Herschel seem to prove that the pure colours of the spectrum are red , green , 
and blue; that the mixture of yellow and blue cannot in any way be made to 
produce green, but one of red and green will form yellow. 
In the year 1802 the far-sighted Wollaston, instead of passing the beam of 
light through a circular orifice, made use of a slit — inch wide, the sides of 
which were parallel to those of a flint-glass prism. To his astonishment, in¬ 
stead of a continuous band of colours, the spectrum was crossed by six dark 
lines. 
Thirteen years afterwards, M. Fraunhofer, of Munich, found that instead of 
six, he could map out more than six hundred, and discovered the important fact 
that these lines were always exactly constant, both in number and position, and. 
consequently ever since they have been, called “ Fraunhofer’s linesj” 
