On Water and Air. 
[August, 
5io 
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 VI. 
f N our last lecture we entered upon the examination of 
air, and I confined myself in that examination to what 
we call the physical properties of air, not going into 
its chemical qualities. We learnt how the pressure of the 
atmosphere was determined, — how that immortal experiment 
of Torricelli was made ; and, as I said at the time, I think 
that no more impressive experiment ever could have been 
made, or at least that there was no greater example of that 
outgoing, so to say, of the human mind in advance of expe- 
riment, than in the case of Torricelli. It was an instance 
of pure reasoning by which he inferred that a mercury 
column 30 inches high would be supported by the pressure 
of the atmosphere. His seeing this beforehand, and his 
bringing his foresight to the test of fadt, and seeing that 
fa dt realised and experienced, must have given him a joy 
and pleasure not frequently experienced. 
Well, this was in 1654 ; but immediately afterwards the 
discovery of the air-pump placed in the hands of investi- 
gators a means of pursuing this subject farther, and one 
great man — a man whose name is for ever memorable — 
threw himself with ardour at the time into the investigation 
of this subjedt. This was the illustrious Robert Boyle. 
He improved the air-pump, and he made a great number of 
experiments with his improved “pneumatic machine,” as it 
was called sometimes. He was a man of great thought and 
great power of experiment, and great reasoning power. 
Herein consists the power of a philosopher in examining 
N ature — that he shall have power not only to investigate 
the fadts of Nature by inventing experiments, but the power 
of reasoning out those experiments to their legitimate 
results. Boyle possessed both these qualities in a high 
* Being a Course of Six Le&ures adapted to a Juvenile Auditory, delivered 
at the Royal Institution of Great Britain, Christmas, 1879. Specially re- 
ported for “ The Journal of Science. • 
