Flame and the effluvia of flaming bodies,[[10]]
Ice and snow—but not below the temperature of 13° Fahrenheit.
Earthy and stony substances, of which the hardest are the worst.
Glass filled with boiling water,
Vapour or steam of boiling water,
Smoke.
All compounds which contain the above substances in different proportions, are conductors in different degrees.
Non-conductors or electrics.
Glass and all vitrifications; even those of metals.
All gems, of which the most transparent are generally the best.