August 12,1871.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
135 
trum analysis an impulse to which, in a great measure, 
is due its splendidly successful cultivation by the labours 
of many able investigators within the last ten years. 
To prodigious and wearing toil of Kirchhotf himself, 
and of Angstrom, we owe large-scale maps of the solar 
spectrum, incomparably superior, in minuteness and 
accuracy of delineation, to anything ever attempted 
previously. These maps now constitute the standards of 
reference for all workers in the field. Plucker and Hit- 
torf opened ground in advancing the physics of spectrum 
analysis and made the important discovery of changes in 
the spectra of ignited gases, produced by changes in the 
physical condition of the gas. The scientific value of 
the meetings of the British Association is well illustrated 
by the fact that it was through conversation with Pliicker, 
-at the Newcastle meeting, that Lockycr was first led into 
the investigation of the effects of varied pressure on the 
quality of the light emitted by glowing gas, which he 
•and Erankland have prosecuted with such admirable 
success. Scientific wealth tends to accumulation accord- ( 
ing to the law of compound interest. Every addition to 
knowledge of properties of matter supplies the naturalist 
with new instrumental means for discovering and inter¬ 
preting phenomena of nature, which in their turn afford 
foundations for fresh generalizations, bringing gains of 
permanent value into the great storehouse Of philosophy. 
Thus Erankland, led, from observing the want of bright¬ 
ness of a candle burning in a tent on the summit of 
JMont Blanc, to scrutinize Davy’s theory of flame, dis¬ 
covered that brightness, without incandescent solid par¬ 
ticles, is given to a purely gaseous flame by augmented 
pressure, and that a dense ignited gas gives a spectrum 
comparable with that of the light from an incandescent 
solid or liquid. Lockyer joined him, and the two found 
that every incandescent substance gives a continuous 
spectrum; that an incandescent gas under varied pres¬ 
sure gives bright bars across the continuous spectrum, 
some of which, from the sharp, hard and fast lines 
-observed where the gas is in a state of extreme attenua¬ 
tion, broaden out on each side into nebulous bands as 
the density is increased, and are ultimately lost in the 
continuous spectrum when the condensation is pushed on 
till the gas becomes a fluid no longer to be called gaseous. 
More recently they have examined the influence of tem¬ 
perature, and have obtained results which seem to show 
that a highly attenuated gas, which at a high tempera¬ 
ture gives several bright lines, gives a smaller and smaller 
number of lines, of sufficient brightness to be visible, 
when the temperature is lowered, the density being kept 
unchanged. 
Stokes’s dynamical theory supplies the key to the 
philosophy of Frankland and Lockyer’s discovery. Any 
ntom of gas when struck and left to itself vibratos with 
perfect purity its fundamental note or notes. In a highly 
attenuated gas each atom is very rarely in collision with 
other atoms, and therefore is nearly at all times in a 
state of true vibration. Hence the spectrum of a highly 
attenuated gas consists of one or more perfectly sharp 
bright lines, with a scarcely perceptible continuous gra¬ 
dation of prismatic colour. In denser gas each atom is 
frequently in collision, but still is for much more time 
free, in intervals between collisions, than engaged in 
•collision; so that not only is the atom itself thrown 
sensibly out of tune during a sensible proportion of its 
whole time, but the confused jangle of vibrations in 
•every variety of period during the actual collision 
becomes more considerable in its influence. Hence 
bright lines in the spectrum broaden out somewhat, and 
the continuous spectrum becomes less faint. In still 
denser gas each atom may be almost as much time in 
•collision as free, and the spectrum then consists of broad 
nebulous bands crossing a continuous spectrum of con¬ 
siderable brightness. When the medium is so dense that 
each atom is always in collision—that is to say, never 
free from influence of its neighbours—the spectrum will 
generally be continuous, and may present little or no 
appearance of bands, or even of maxima of brightness. 
In this condition the fluid can be no longer regarded as 
a gas, and we must judge of its relation to the vaporous 
or liquid states according to the critical conditions dis¬ 
covered by Andrews. 
While these great investigations of properties of mat¬ 
ter were going on, naturalists were not idle with the 
newly-recognized power of the spectroscope at their ser¬ 
vice. Chemists soon followed the example of Bimsen in 
discovering new' metals in terrestrial matter by the old 
blow'-pipe and prism test of Fox Talbot and Herschel. 
Biologists applied spectrum analysis to animal and vege¬ 
table chemistry, and to sanitary investigations. But it 
is in astronomy that spectroscopic research has been 
carried on with the greatest activity, and been most 
richly rewarded with results. The chemist and the 
astronomer have joined their forces. An astronomical 
observatory has now’- appended to it a stock of reagents 
such as hitherto was only to be found in the chemical 
laboratory. A devoted corps of volunteers of all nations, 
whose motto might well be ubique , have directed their 
artillery to every region of the universe. The sun, the 
spots on his surface, the corona and the red and yellow 
prominences seen round him during total eclipses, the 
moon, the planets, comets, auroras, nebulae, wdiite stars, 
yellow stars, red stars, variable and temporary stars, 
each tested by the prism w r as compelled to show its 
distinguishing prismatic colours. Rarely before in the 
history of science has enthusiastic perseverance, directed 
by penetrative genius, produced within ten years so 
brilliant a succession of discoveries. It is not merely 
the chemistry of sun and stars, as first suggested, that is 
subjected to analysis by the spectroscope. Their whole 
laws of being are now subjects of direct investigation; 
and already we have glimpses of their evolutional history 
through the stupendous powder of this most subtle and 
delicate test. We had only solar and stellar chemistry; 
w r e now have solar and stellar physiology. 
It is an old idea that the colour of a star may bo 
influenced by its motion relatively to the eye of the 
spectator, so as to be tinged wdth red if it moves from 
the earth, or blue if it moves towards the earth. 
William Allen Miller, Huggins and Maxwell show r ed 
how r , by aid of the spectroscope, this idea may be made 
the foundation of a method of measuring the relative 
velocity with wdiich a star approaches to or recedes from 
the earth. The principle is, first to identify, if possible, 
one or more of the lines in the spectrum of the star, with 
a line or lines in the spectrum of sodium, or some other 
terrestrial substance, and then (by observing the star 
and the artificial light simultaneously by the same 
spectroscope) to find the difference, if any, between 
their refrangibilities. From this difference of refrangi- 
bility the ratio of the periods of the tw*o lights is cal¬ 
culated, according to data determined by Fraunhofer 
from comparisons between the positions of the dark 
lines in the prismatic spectrum and in his own “ inter¬ 
ference spectrum” (produced by substituting for the 
prism a fine grating). A first comparatively rough 
application of the test by Miller and Huggins to a large 
number of the principal stars of our skies, proved 
that not one of them had so great a velocity as 315 
kilometres per second to or from the earth, which is a 
most momentous result in respect to cosmical dynamics. 
Afterwards Huggins made special observations of the 
velocity test, and succeeded in making the measurement 
in one case, that of Sirius, w T hich he then found to be 
receding from the earth at the rate of 66 kilometres per 
second. This, corrected for the velocity of the earth at 
the time of the observation, gave a velocity of Sirius, 
relatively to the sun, amounting to 47 kilometres per 
second. 
During six or eight precious minutes of time, spectro¬ 
scopes have been applied to the solar atmosphere and to 
the corona seen round the dark disk of the moon eclips¬ 
ing the sun. Some of the wonderful results of such. 
