Meteorology, 91 



with those figured by Scoresby ; but /, m, w, o, and /), are those of his which 

 come nearest to the English ones. — Cacale. Cambridge^ Feb. 12. 1830. 



Anchor Frosts. — Jan. 22. 1828. The state of the weather forms a prin- 

 cipal part of our every-day conversation ; much of our personal comfort, 

 and very often our health, depends on it. The approach of winter is par- 

 ticularly felt, for 



— - " This is the season when 

 An icy gale, oft shifting, o'er the pool 

 Breathes a blue film, and in its mid career 

 Arrests the bickering stream : " Thomson. 



and which sometimes takes place in a wonderful manner. It is necessary 

 to premise that it is as natural for the element of water to be solid as fluid, 

 and that its fluidity only depends on that temperature of the atmosphere 

 which is marked by Fahrenheit's thermometer at the thirty-third degree : 

 at and above this point, water is fluid; and, below, it is solid, or in the state 

 of ice. From the short days, and oblique direction of the sunbeams, the 

 heat received by the surface of the earth in the day is soon radiated ofi', 

 and the colder air from the higher regions of the sky descends and reposes 

 on the surface of the ground. At the same time, too, if the face of the 

 ground becomes incrusted by frost, the natural heat of the earth is pre- 

 vented from escaping to increase the temperature of the air, and this being 

 cooled down to the thirty-second degree, water becomes congealed, and, as 

 the poet has said, the rapid river is even arrested in its course. In ordi- 

 nary cases, the crystallisation begins on the surface j on every part simul- 

 taneously on stagnant pools, if the air be perfectly calm ,* but on water in 

 motion, whether as that of a stream, or when ruffled by wind, the crystal- 

 lisation begins at the sides, and gradually shoots across the surface, till the 

 whole is a connected plate, and, in continued frost, increases in thickness 

 from below. But great bodies of ice are formed, and stop the current of 

 rivers, in a very difierent way, and this, when it happens, is called by the 

 owners of water-mills an anchor frost. In this the ice begins to form at the 

 bottom of the stream (it never happening in pools or stagnant water), 

 instead of on the surface. This unusual phenomenon, so contrary to our 

 common ideas respecting the action of frost, may, however, be rationally 

 accounted for by any one who has attended to it. The streams in which 

 anchor frosts are most commonly seen are such as contain water of different 

 temperatures, viz. surface drainage and land springs, and supplies from 

 main springs. The first are always several degrees colder in winter than 

 the latter, which is never less than 40°, even in the severest frosts. This 

 mixed stream is partially affected by the air when below the freezing point. 

 The colder globules are first frozen, shoot into crystals of various shapes, 

 jand may be seen floating on the surface individually, and are prevented 

 coalescing by the intermediate main spring water, which, although warmer, 

 does not entirely dissolve the already frozen particles. In the deeper parts 

 of the river no accumulation of these crystals is visible; but in the shallows, 

 where the water percolates through or over a pebbly bottom, there the crys- 

 tals are intercepted between the interstices of the stones, and then become 

 heaped together in thick beds, so as even to throw the current out of its 

 channel. At the gratings of the water-gates of mills, the spicula are also 

 accumulated, and are greater annoyances to the miller than the thickest 

 ice on the surface of the mill-pond, because of the difficulty of clearing it 

 away. The fact of the crystals of ice (which are specifically much lighter 

 than water) sinking below the surface, is an attending circumstance which 

 requires explanation. They do not sink from theii- specific gravity, but in 

 the commotion of the current they are occasionally submersed, and while 

 so are stopped by any obstruction, where they commence and compose the 

 aggregation. — /. ilf. Ja«.22. 1831. 



