three o'clock
The thick wooden side of the tub is a poor conductor ; the ice that has formed over the surface is even a worse , and so the water within is shielded from the cold . It therefore almost ceases to freeze , and so becomes of no practical use . An intelligent understanding of these principles is of great practical value . If I could have waked up and placed another tub of water in the room at two or three o'clock , or else taken all of the ice out of the first one , the process of freezing and giving out heat would have gone on rapidly again , and none of the plants would have suffered . I have heard people say that putting water in a cellar was all a humbug -- that the water froze and the vegetables also . Of course the vegetables froze after the water congealed , or the cellar may have been so defective that both froze at the same time . The latent heat given out by a small amount of freezing water can not counteract any great severity of frost . ''