x88o.] 
On Water and Air, 
,179 
ON WATER AND AIR.* 
By John Tyndall, D.C.L., LL.D., F.R.S., 
Professor of Natural Philosophy at the Royal Institution 
of Great Britain. 
Lecture III. 
WANT you to be able to associate with every term 
that I employ in these lectures a perfectly definite 
meaning. If I speak of things in science, I wish you 
to be able to present before your minds an image of 
what I am speaking of. Now, there are various terms that 
I am afraid I must employ, and therefore it is my duty to 
try and make clear to you exactly what I mean by those 
terms. 
After a vast amount of experiment and of thought, philo- 
sophers have come to the conclusion that all bodies are com- 
posed of what we call “ smallest parts.” An ancient philo- 
sopher and poet used to call them “ first beginnings.” I 
say that all bodies are composed of these exceedingly small 
parts — the smallest into which a body can be divided. They 
are beyond the range of all microscopes, but still we see 
them with the mind’s eye, though they cannot be seen with 
the eye of the body. These parts are called “ atoms.” I 
shall have immediately in this jar a collection of atoms of 
oxygen gas, which I will pour into the jar from this bottle. 
The atoms will fill the jar. Mr. Cottrell will open the bottle 
so as to allow a quantity of the atoms to issue. The jar is, 
as you see, placed upright, and the gas being slightly 
heavier than air falls into it, and it is rapidly filled. I will 
now make it evident to you that I have in the jar the thing 
which we call oxygen gas. [The jar was filled with oxygen 
as indicated. A piece of wood was then ignited and plunged 
into the gas, with the usual result of a strongly intensified 
combustion.] 
If I dip this glowing splinter of wood into the jar, you see 
that it immediately bursts into flame. The oxygen is 
capable of producing this combustion. 
Being a Course of Six Ledtures adapted to a Juvenile Auditory, delivered 
at the Royal Institution of Great Britain, Christmas, 1879. Specially re- 
ported for “ The Journal of Science.’ 5 
O 2 
