A HARD-WORKING DIET. 5 
behaving, but where it is not convenient to do this, 
perhaps it is still possible to convey some ideas about 
them, if not very complete and exact. 
To those who feel, 
“A fire’s a good companionable friend, 
Who meets your face with welcome glad,” 
and love to loiter in the gloaming and gaze into it, 
OXYGEN is a perfectly familiar though unseen friend. Oxygen. 
The old adage “seeing is believing” is taken by 
some as equivalent to “do not believe what you 
cannot see.” But we believe in many things we 
cannot see, when we can see what they do. We cannot 
see the wind, but we are constrained to believe in it 
if it brings a chimney pot down through the roof. 
When, sheltered by a window, we watch the boughs 
swaying and the clouds scudding along in fantastic 
forms, or perhaps smile at undignified chases after 
runaway hats, we do not hesitate to say “see what 
a wind there is!” 
Oxygen is a perfectly familiar gas, because any one 
watching a fire is seeing one of the things the unseen 
Oxygen is always somewhere doing. One-fifth of the 
air is free Oxygen. Every one knows that a fire ora 
lamp will not burn without air, though they may not 
know that it is only the Oxygen of the air that is con- 
cerned in the burning. The rest of the air has nothing 
to do with it so far as we know. In pure Oxygen, 
which can be obtained in several ways, burning is 
much more brilliant. The burning of a watchspring 
in Oxygen is a sight young and old enjoy, for as a 
professor at the Royal Institution used to say to his 
audience, one is never tired of seeing it. 
