The Boy Mechanic, vol. 1, page 338
Take a piece of very clear ice and melt it down into the hollow of your hands so as to form a large lens. The illustration shows how this is done. With the lens-shaped ice used in the same manner as a reading glass to direct the sun's rays on paper or shavings you can start a fire. - Contributed by Arthur E. Joerin.
“For the word of God is living and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart.”
– Hebrews 4:12