574 



J. CLIFTON WAED ON THE GRANITIC, GRANITOID, AND 



•116 



•142 



No. 3. -< -132 y 

 154 

 154 

 ^•166, 



141 No. 4. «< 



143 



•132"] 

 •180 

 •104 

 •200 

 •125 

 •116 

 •125 

 •132 

 •142 

 •166 

 •154 K 

 •100 

 •166 

 •142 

 •132 

 •142 

 •166 

 •154 

 •132 

 i v -166J 



Although there is here considerable diversity of measurement in 

 the two groups, the means are strikingly similar. If the measure- 

 ments of *180 and *200 in No. 4 are struck out as probable errors, 

 the mean is reduced to *138, which, considering the number of 

 measurements still below this, is probably yet slightly too high. 



In some of the smallest liquid- cavities the vacuity is so small that 

 it looks merely like a black spot moving rapidly about. In one such 

 instance there was the appearance as of two bubbles connected 

 moving about together. These very active spontaneous movements 

 are most curious to watch. In many cases the little bubble seems 

 never to be at rest ; nor can I make out that shaking of the micro- 

 scope-stage has any effect upon the movements, whether they be 

 active or more sluggish. Mr. Bonney suggested to me that the 

 motion might be caused by currents set up in the liquid by unequal 

 heating ; I can scarcely fancy, however, that this can be the case, 

 since the liquid-cavities in which the most marked movement takes 

 place are generally so extremely small (often less than y^J^-j- of an 

 inch in diameter) and the motion is so irregular. 



The larger bubbles, which probably contain air or gas, do not 

 exhibit these active movements; very generally also these larger 

 bubbles are attached to one side of the liquid-cavity, and sometimes 

 markedly drawn out or flattened, as is seen in figs. 1, 41, and 68. 



Occasionally small crystals are found in the liquid -cavities besides 

 the vacuity, as figured in Mr. Sorby's memoir ; and long fine crystals, 

 probably of schorl, sometimes pass quite through the walls of the 

 cavities, as in figs. 37 and 38. 



Eor the most part the liquid- cavities containing moving vacuities, 

 which alone are reliable for measurement, are extremely small, 

 sometimes less than yg-^nr of an inch in diameter. Much larger 



