ON THE STRUCTURE OF GLACIER ICE 487 



Spheroidal. The strangest thing is, however, that M. Agassiz has 

 taken the air-bubbles for drops of water, and the drops of water for 

 air-bubbles, as any one who is familiar with the microscopic appearance 

 of bubbles of air will see, on comparing the description in (7) with 

 the figure 10. In the next place, I repeatedly exposed thin plates of 

 ice to the sun, carefully watching the air-bubbles, without being able 

 to observe the phaenomena detailed by M. Agassiz in (6) ; and I must 

 frankly confess I do not understand how such changes as those 

 described are reconcileable with the commonest properties of ice and 

 air. How do the bubbles enlarge when exposed to the sun? ]\I. 

 Agassiz has already admitted that the chambers are closed (i), and we 

 know that ice is not readibly distensible ; and therefore I hold it 

 to be impossible that the bubbles should visibly dilate before the 

 melting of the adjacent ice ; and as to enlarging by the melting of 

 the ice-wall, the fractional difference between the volume of water 

 and the ice from which it proceeds, would be wholly imperceptible on 

 such a scale. With regard to the explanation of the crackling noise 

 given in (3), I can only say that I have repeatedly watched a thin 

 lamina of ice melting, both by transmitted and reflected light, and 

 that I have seen the walls of the chambers reduced to the thinnest 

 pellicle without being broken by pressure from within. The air- 

 bubbles escape quite quietly as soon as their wall is perforated. 

 Furthermore, the cavities left where the air-bubbles have been, are 

 not fissures at all, but, as I have said above, rounded pits. Indeed, 

 this is a necessary consequence from M. Agassiz's own statements 

 with regard to the shape of the bubbles. 



M. Agassiz affirms in (5), that ice brought up from a depth of 65 

 metres was perfectly similar in structure to that represented in his 

 figure 10. The fact is important ; but surely it alone affords sufficient 

 evidence that " diathermanicity " has nothing to do with the formation 

 of the cavities and their watery contents. And indeed in (4) this 

 same piece of ice (fig. 10) is said to have come from the " gallery of 

 infiltration," a cavity perfectly shaded, and bored many feet belo^v 

 the surface of the glacier. So that either this figure does not 

 represent the structure of the glacier at this point, or the structure is 

 unaltered, and diathermanicity has nothing to do with it. 



It follows, therefore, that there is no evidence to show that the 

 influence of solar radiation has anything to do with the structure ; on 

 the contrary, M. Agassiz's /«^^j- strengthen my case. 



If it be the universal character of glacier ice to be full of closed 

 cavities containing fluid water and air, it becomes a matter of extreme 

 interest to ascertain how the air and the water come there ; how it i.s 



