the vapour to escape from the centre to the edges of the drop; and this resistance may be increased till the vapour finds it easier to break in bubbles through the middle of the drop than to escape laterally.
"All these facts are in perfect harmony with the explanation, that it is the development and incessant removal of a steam-spring at the lower surface of the drop which keeps the liquid from contact with the metal and shields it from the communication of heat by contact. Owing to this, indeed, the liquid in the spheroidal condition never reaches its boiling temperature. If you plunge a thermometer into a spheroid of water in a red-hot vessel, its temperature will be found to be several degrees under 212°. When the lamp is withdrawn and the basin cools, the tension of the steam underneath the drop becomes gradually feebler. The spring loses its force, the drop sinks and finally comes in contact with the metal. Heat is then suddenly imparted to the liquid, which immediately bursts into ebullition."
It is well known that we may introduce the hand, if moist, into melted lead, nay, into white-hot melted copper or iron, and move it slowly about in thee liquids, not only without burning the hand, but without even feeling the intense heat of the melted metals; whereas iron or copper at a heat far below redness, instantly causes a blister or burn. This