went on in the lecture room when he was not present, he was wholly at sea regarding the drops. He had a hazy idea regarding them, however, and resolved to hazard a recitation. It was better than complete failure.
As "every schoolboy" (to quote a well known authority) knows what the Prince Rupert drops are, I will only state that they are globules of glass, pear shaped, with a long thin "tail" of the same brittle material. They are formed by dropping molten glass into water. The outside cools quickly, a long tail is formed, and there results an unequal strain on the glass, because the outside part has cooled faster than the inside. The instant a small part of the "tail" is broken off, the entire drop crumbles to glass-dust, the pressure once more being equalized.
It was this object and phenomenon that Dutch was called on to recite about. He rose in his seat, and began with an air of confidence that he did not feel:
"The Rupert drops illustrate the power of hot water or steam. They are globules of glass, filled with water, and, when they are heated, they burst to pieces, showing the expansive force of heat."
The class wanted to roar. Dr. Churchill raised his eyebrows in surprise. Dutch had described another glass object used in the class room, and his explanation of that had been correct, but it was
