PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 967 



Deep ponds and lakes are slow in freezing, ])ecanse the whole 

 body of the water is slow in attaining the maximum density by 

 cold ; and until this is done the surface cannot sink to 32" Fiijj. 

 On the other hand, rivers and streams are slower in freezing than 

 stagnant shallow water, the motion interfering with convection 

 and also with crystalization. Ponds and lakes are often fed hy 

 springs and streams, so that if the former be frozen on the surface 

 the latter may be active; and if they find their way into ice-bound 

 water, they will carry in much air. In small collections of wat^', 

 where the temperature is low enough to lock up the springs, air 

 may be supplied b}^ a portion of the water sinking into the soil. 

 Action like this is seen on country roads, when a sharp frost sets 

 in after rain. The water that collects in the wheel ruts, &£,., 

 freezes at the surface in blades of ice that cross at angles of 6j0. 

 If this ice be tapped with a stick a few hours after, it will be found 

 to cover a hollow space, from which the water has been al)sorbed 

 by the soil. If water thus settles away beneath a frozen ponxl, 

 the ice is left unsupported, except at its edges, and the air would 

 surely find its way l>eneath it either through cracks in the ice tor 

 through the soil. 



Colored Eain. 



Mr. H. L. Eades, of South Union, Ky., states in The Scientific 

 American that on the night of the 12th of March last, there was 

 a copious fall of rain and vessels left in the open air were found in 

 the morning to contain water impregnated with a yellow suljstance; 

 a specimen of it was sent to the editors, which has been subjected 

 to a microscopic examination l)y Dr. Dinwiddle, and found to con- 

 sist of a species of pollen, probably from the pitch pine. 



An article by Edwin Durkin, of the Royal Observatory of Gre^i- 

 with, has lately appeared, from which we select the following 

 instances of apparently colored rain and snow in comparatively 

 modern times. The first was a memorable example of colored 

 rain known to have fallen at night in the Hague in 1G70. People 

 of all classes were affected by this mystcriouji rain of ]jlood, which 

 they regarded as a miraculous act of Providence, foretellinir sceires 

 of approaching war. There happened to be a physician in the 

 town whose scientific curiosity urged him to inquire into the cause 

 of this wonderful phenomenon. He examined some of the vr^v&v 

 with a microscope, and found that it had not really changed color, 

 but that the blood-red was produced by swarms of red animals br 



