Qreen Ice. 53 



may demand, in order to be frozen, a somewhat lower tempe- 

 rature than that in which the water solidifies. When the mass 

 of ice became warmer, and its outside was actively thawing, I 

 imagine the conducted heat was arrested by the conferva, 

 and thus the water-blebs round it gradually formed. If this 

 were the case, the minutes air-bubble which I saw in some in- 

 stances attached to the conferva, should have collapsed as the 

 ice surrounding it thawed. I had not the means of ascer- 

 taining this, but the escape of the larger air-bubbles was a 

 pretty sight when a lump of the ice was placed in. a tumbler of 

 warm water, and the melting process watched under a lens. 



I believe Ehrenberg ascribed the escape of animalcules from 

 being frozen to death when the water in which they lived con- 

 gealed, to the action of their vital heat ; but it seems to me 

 more probable that they escaped because their vital fluids dif- 

 fered sufficiently from water to freeze at a lower temperature. 

 Professor Tyndal, in the work cited, observes that there " seems 

 no such thing as perfect homogeneity in nature. Change com- 

 mences at distinct centres, instead of being uniformly and con- 

 tinuously distributed The melting temperature of ice 



is set down at 32° F., but the absence of perfect homogeneity, 

 whether from difference of crystalline texture, or some other 

 cause, makes the melting temperature oscillate to a slight 

 extent on both sides of the ordinary standard/'' It may be that 

 slight variations from that uniformity of condition which is 

 described by the term " homogeneous," causes some particles 

 of water to freeze quicker than others; and if so, we may 

 imagine how slight a divergence in the molecular condition or 

 composition of a fluid, from the condition and composition of 

 water, may enable the liquid contents of a plant or animal to 

 retain their fluidity when the water in which they are immersed 

 takes the solid form. 



The question of why so little green stuff deposited in patches 

 considerably distant from each other, gave so deep a tint to 

 the ice of my experiments, may perhaps be answered by reference 

 to its heterogeneous structure. There must not only have been 

 refractions but also reflexions in all sorts of directions, from 

 crystalline surfaces in various planes. Thus I conceive the 

 effect of a very little green stuff was made to go a great way. 

 The explanation may not be correct, but I can think of no 

 better, and perhaps the remarks I have thrown together may 

 suggest observations and experiments to others, who may 

 witness appearances of the same or a similar kind. 



