338 F. A. Perret — Circulatory /System in the 



a surrounding " shore " of solid material congealed to the sides 

 of the pit. The lake is active by the continuous emission of 

 gas and especially through the irruption, and eruption, of very 

 large bubbles which, coalescent in the depths of the conduit, 

 rise with great buoyancy and form those beauteous fountains 

 of lava, to the study of which a preceding paper has been 

 devoted.* This particular form of activity is, however, of an 

 intermittent character and is limited to certain portions of the 

 lake upon whose general surface there forms, by cooling in 

 contact with air, a film or skin, flexible while thin but often 

 thickening to a solid crust which is brittle and readily broken 

 by uneven pressure. As these congelations occur in spite of 

 the ordinary supply of juvenile gas, it is highly probable that, 

 were it not for some other preventive cause, the inward con- 

 solidation from the walls and the downward incrustation from 

 the surface would continue progressively until the entire mass 

 became solid. 



This preventive cause consists of a grand movement of 

 translation in the lava of the lake — a powerful system of cir- 

 culation which stirs the entire mass of liquid, impeding deposi- 

 tion upon the walls and preventing the formation, for any 

 length of time, of a thick, immovable crust upon the surface. 

 In importance, therefore, this phenomenon will be seen to be 

 second to none and to merit the devotion of a paper to its 

 exclusive study. 



It is natural, in such cases, to seek analogy in some familiar 

 or easily tried experiment, and this is here found in a vessel of 

 water heated from below. Expanded by the heat, the lower 

 liquid rises to the surface, spreads and descends by the cooler 

 sides, and when ebullition occurs, the expansive effect of the 

 gas bubbles, together with their buoyancy, adds ascensional 

 power to the rising column, thus establishing a system of con- 

 vection by which the entire mass is stirred — why not, therefore, 

 under essentially similar conditions in the crater, a similarly 

 simple and easily explainable principle of action ? But it is in 

 precisely this manner that many long-lived errors have crept 

 into science, whose history has shown the necessity of inves- 

 tigating the phenomenon itself instead of studying an imitation, 

 however temptingly analogous. 



The merest glance at the normal lava lake at Halemaumau 

 suffices to show that it has a longer and a shorter diameter and 

 that the surface material is moving in the general direction of 

 its length. We shall see later that these conditions are not 

 fortuitous but are the necessary consequence of the working 

 principle of the circulatory system. During the entire sum- 

 mer of 1911, excepting for a few hours on August 9th and 



* This Journal, February, 1913. 



