342 F. A. Per ret — Circulatory System in the 



several caves or "spatter-grottoes" situated at the margin of 

 the lake, the division of flow producing a striation of the sur- 

 face skin, occasionally, but not frequently, as complicated as 

 that shown in fig. 2. These grottoes are, in part, eroded in 

 the banks by the large bubbles of juvenile gas ascending from 

 the conduit, but are chiefly formed by the arching over of a 

 roof built of the congealed spatterings of lava scattered by the 

 bursting bubbles of gas. They are, therefore, peripheral 

 fountains, as contrasted with the central type, and their action, 

 while more nearly continuous, is essentially similar, producing 

 a lower level within the grotto into which the surface layers 

 flow, turn downward, and descend. Once this action is started 

 it will be accelerated and maintained by the downpull of the 

 vertically descending heavy layers which act as a sort of semi- 

 solid syphon of which the long arm is the descending sheet 

 and the short arm is represented by the surface layers, actually 

 longer but easily drawn by reason of their horizontal position. 

 The suction is sometimes so strong as to produce a veritable 

 maelstrom with a local surface flow resembling a mill-race, and 

 it is this powerful downflow of the heavy surface layers which 

 is the immediate cause of the great movement of translation 

 and of the whole system of circulation. JSTo mere difference 

 of surface levels could produce such rapid flows — often reach- 

 ing four meters per second in a mill-race and frequently 

 exceeding sixty meters per minute on the general surface of 

 the lake — while convection, in the sense of a rising column of 

 heated and vesiculated lava, although not absent as we shall 

 see later, plays a role which must be considered as secondary. 

 The indirect but true primal cause lies, of course, in the 

 ascent of the great bubbles and it will seem strange to the 

 reader, as it has to observers, that these rise where the lava is 

 descending. In reality, however, it is the lava which flows to 

 and descends at those localities where the level is lowered by 

 the escape of the gas bubbles. William Lowthian Green, in 

 attempting to account for most of the Hawaiian phenomena 

 on a non-gaseous basis,* held that the violent jetting of the 

 lava at the places of descent was due to air being carried down 

 with the lava and, expanded by the heat, again bursting its 

 way to the surface. This ingenious explanation is negatived 

 by the fact that the escaping gas burns in contact with the 

 atmosphere, the flames, under certain circumstances, being 

 always and easily visible at night. Jets of flame Hve meters 

 in length often flash from a spatter grotto upon the bursting 

 of a large gas bubble within while smaller jets burn steadily at 

 broken portions of its overhanging roof. The present writer 



* "Vestiges of the Molten Globe," by Wm. Lowthian Green, Honolulu, 

 1887. 



