352 
UTILITY OF THE STUDY OF CHEMISTRY. 
est of them distant more than half a million 
of miles ? Our first inquiry shall then be. 
What is the probable Distance of 
THE FIXED Stars ? 
Are they, as we are told, many millions of 
miles away from us ; so far, indeed, that their 
light, travelling as it does at the rate of 
80,000 leagues in a second, has from the 
nearest been six or eight years in reaching 
us ? And if it be so, how is this known ? 
Let us suppose an observer to have travel- 
led about, far and wide, on the earth’s sur- 
face, and accurately to have observed, as he 
went on, the appearances of the heavens ; he 
will at once have perceived the stars to be 
bodies scattered about in that great space, 
whatever it may be, which contains the earth, 
and he will have remarked that they do not 
alter their apparent relative positions, as he 
moves about on it. Their apparent positions, 
with regard to the horizon, are, indeed, con- 
tinually altering; but with regard to one 
another, he finds them always the same. 
This will appear to him very extraordinary, 
when he considers that the various objects 
around him on the earth’s surface, are conti- 
nually subject to apparent changes of rela- 
tive position, as he moves about from one 
place to another. Thus for instance — let him 
be sailing along the sea-coast at night, and 
let him observe two lights upon projections 
of the shore. At one instant, when he is in 
the line joining the lights, they will appear 
to him to coincide, blending momentarily 
into one light ; as he proceeds, they will ap- 
pear to separate, or, in the nautical phrase, 
they will open ; and this opening of the lights 
will continue, until they have at length ac- 
quired a certain maximum apparent distance. 
They will then appear to approach one ano- 
ther ; and, as he finally leaves them behind 
him, they will go through all the same circum- 
stances of apparent motion as attended his 
approach to them. If the lights be suffi- 
ciently remote, all these changes in their ap- 
parent distance from one another, will be re- 
ferred to, and apparently take place upon, 
the circular margin of the horizon. They 
will seeiu like two beads of light moving to- 
wards one another on the circumference of 
that circle ; coinciding, then receding, and 
again approximating to one another.^ These 
apparent motions are called parallactic.* 
(To he continued.) 
* Parallax, the angle formed by two differ- 
ent lines of view drawn towards one and the 
same object. Suppose a point is seen from 
the two ends of a straight line, the two lines 
of view towards that point form, with the first 
line, a triangle, whose angle at the point seen 
is the parallax, or parallactic angle. Annual 
paraHaa?- the angle formed by two lines from 
the ends of one of the diameters of the earth’s 
orbit to a fixed star, which angle, on account of 
the immense distance of the fixed star, is too 
small to be observed. 
CHEMISTRY. 
THE WONDERFUL AND SUDDEN TRANS- 
FORMATIONS WITH WHICH CHEMISTRY IS 
CONVERSANT, THE VIOLENT ACTIVITY 
OFTEN ASSUMED BY SUBSTANCES USUAL- 
LY CONSIDERED THE MOST INERT AND 
SLUGGISH, AND, ABOVE ALL, THE INSIGHT 
IT GIVES INTO THE NATURE OF INNUME- 
RABLE OPERATIONS WHICH WE SEE DAILY 
CARRIED ON AROUND US, HAVE CONTRI- 
BUTED TO RENDER IT THE MOST PO- 
PULAR, AS IT IS ONE OF THE MOST EX- 
TENSIVELY USEFUL, OF THE SCIENCES ; 
AND WE SHALL, ACCORDINGLY, FIND NONE 
WHICH HAVE SPRUNG FORWARD, DURING 
THE LAST CENTURY, WITH SUCH EXTRA- 
ORDINARY VIGOUR, AND HAVE HAD SUCH 
EXTENSIVE INFLUENCE IN PROMOTING A 
CORRESPONDING PROGRESS IN OTHERS. — 
Sir John Herschel on the Study of Natural 
Philosophy. 
Chemistry is the art wherby compound 
bodies are changed into simple ones, or simple 
bodies into compounds. The former of these 
processes is called Analysis or Decomposition, 
and the latter Synthesis or Composition. 
As a science, it is the province of Chemistry to 
determine the chemical relation of simple 
bodies, and the structure and chemical rela- 
tions of compounds. Few of the operations of 
Chemistry, which are employed for the attain- 
ment of these objects, are either purely ana- 
lytic or synthetic ; a combination of these 
methods generally taking place in the pro- 
cesses of the chemist. 
Different kinds of matter, which are the ob- 
jects of Chemistry, possess certain active pro- 
perties, such as gravity or weight, cohesion, 
elasticity, expansibility, magnetic attraction, 
&c. All these properties are but so many dif- 
ferent modifications of attraction and repul- 
sion. Action, either attractive or repulsive, 
takes place between bodies situated at vari- 
ous distances from each other. Thus the at- 
traction of gravitation operates at indefinite 
and immense distances ; while the attraction 
of cohesion affects the particles of bodies only 
when placed in apparent contact. Repulsive 
action also takes place at different distances. 
Thus, the repulsion between bodies which 
have been subjected to the influence of electri- 
city or magnetism is sufficiently obvious to the 
sight ; and that electric or magnetic sub- 
stances, which repel each other, do not touch, 
may easily be perceived. The expensive pow- 
er of heat, on the other hand, probably af- 
fects particles of matter nearly in contact with 
each other. 
The various phenomena which constitute 
the objects of Chemistry, depend on the opera- 
tion of those modifications of attractive and 
repulsive force, which act on particles of bodies 
placed at insensible distances from each other, 
and are so minute as not to be cognizable by 
our senses, even when assisted by the most 
powerful magnifying glasses. 
There are two species of attraction which 
affect particles of matter when in apparent 
