THE FAIRY-LAND OF SCIENCE. 15 
books to find answers to your questions, you must 
know something of the language they speak. You 
need not learn hard scientific names, for the best 
books have the fewest of these, but you must really 
understand what is meant by ordinary words. 
For example, how few people can really explain 
the difference between a solid, such as the wood of the 
table ; a liquid, as water ; and a gas, such as I can let 
off from this gas-jet by turning the tap. And yet 
any child can make a picture of this in his mind if 
only it has been properly put before him. 
All matter in the world is made up of minute 
parts or particles ; in a solid these particles are locked 
together so tightly that you must tear them forcibly 
apart if you wish to alter the shape of the solid 
piece. If I break or bend this wood I have to force 
the particles to move round each other, and I have 
great difficulty in doing it. But in a liquid, though 
the particles are still held together, they do not cling 
so tightly, but are able to roll or glide round each 
other, so that when you pour water out of a cup on 
to a table, it loses its cuplike shape and spreads itself 
out flat. Lastly, in a gas the particles are no longer 
held together at all, but they try to fly away from 
each other ; and unless you shut a gas in tightly 
and safely, it will soon have spread all over the 
room. 
A solid, therefore, will retain the same bulk and 
shape unless you forcibly alter it ; a liquid will retain 
the same bulk, but not the same shape if it be left 
free ; a gas will not retain either the same bulk or 
the same shape, but will spread over as large a space 
