THE TEMPERATURE 67 



premature hail suddenly devastates the 

 orchards, undoing the long work of spring 

 and summer ; but the thought was pass- 

 ing. Further examination and reflection 

 suggested a reassuring theory. 



When the temperature falls below 

 freezing-point the water in a pond does 

 not begin to solidify immediately. First 

 a thin layer on the surface is chilled and 

 sinks ; then the succeeding layer is chilled 

 and sinks ; then another ; and so on until, 

 under the influence of the cold, the whole 

 body of water, or most of it, has been 

 transfused within itself, and in the pro- 

 cess has reached the freezing-point ; then 

 the forming of ice begins. Until it does 

 begin the mean temperature of the pond 

 is above freezing-point. That, however, 

 could not be said of the Highland stream. 

 Evidence to the contrary was abundant 

 at every step. It might be an exaggera- 

 tion to say that one could actually see 

 the flanges of ice that protruded from the 

 banks extending outwards and gradually 

 narrowing the open space in the middle 



