AuGrsT 2S, 190S] 



SCIENCE 



279 



quantity of vapor expanded may be independ- 

 ent of this rapidity, providing always that 

 the lateral drainage is swfficienily rapid to 

 produce the diference of level. For it is pre- 

 cisely this whicL. makes the difference between 

 a catastrophal eruption of this class and one 

 ■vrhich is merely a phase in the progression of 

 an eruptiTe period Terminal or subterminal 

 lava streams, or the sluggish forms of lateral 

 ontflows can not produce a material reduc- 

 tion in the level of the lava — the former by 

 reason of their location and the latter be- 

 cause the slow drainage is continually com- 

 pensated by alimentation from below; there 

 being no rapid diminution of pr^sure, there 

 is consequently no abnormal expansion. 



In considering further the points of diver- 

 gence between geyser and volcano it would 

 seem that, aside from the obvious dynamic 

 and caloric disproportion — that is, the 

 relative insignificance of the former in size, 

 mechanical power and heat energy — a funda- 

 mental difference lies in the relative propor- 

 tions of water and temperature. In the 

 geyser the heat is moderate while water is 

 abundant and, after an eruption, may freely 

 flow into the central conduit, which it oc- 

 cupies in mass. But in the case of the vol- 

 cano we may imagine that the water can 

 reach the fire-pocket only by capillary infiltra- 

 tion and under snch conditions of tempera- 

 ture and pressure as will cause its intimate 

 union — possibly through complete dissocia- 

 tion — with the heated materials with which 

 it comes in contact, forming thus an incan- 

 descent, eruptive magma. And this will be 

 the case whether the temperature results from 

 chemical combination of the water with oxi- 

 dizable material (Davy), from mechanical 

 friction and compression (ilallet) or from 

 the retained original heat of the earth. The 

 magma will augment in quantity, in tempera- 

 ture and in expansive power with the 

 progressive infiltration of water, and, with its 

 occluded gases will seek a vent at the earth's 

 surface. If there exists, instead, a uni- 

 versal magma with already occluded water 

 gases there will still be the same proportion 

 of water to temperature. 



But what is perhaps the most important 

 point of difference between gej-ser and 

 volcano — and to this all the preceding forms 

 but an introduction — is that in the former, 

 actual eruption is determined and brought 

 about by conditions existing within the geyser 

 itself, while in the latter this is not the case. 

 The geyser is truly automatic, the volcano is 

 not. In studying the development of volcanic 

 eruptions one is irresistibly led to the con- 

 sideration of modifying and controlling forces 

 acting from without and which may even be 

 extra-terrestrial. It is not denied that, given 

 the progressive delivery of active volcanic ma- 

 terial from below, an eruption would in time 

 occur even without external influence, but it 

 is claimed that, under actual conditions, erup- 

 tion will inevitably be precipitated before such 

 a time. If this is true, the study of such 

 modifying influences becomes of the greatest 

 importance, especially in connection with the 

 foretelling of eruptions, and it is only from a 

 profound conviction of its usefulness that the 

 writer ventures to bring forward at this time 

 an old and abandoned bypothesis — that of the 

 luni-solar influence. I believe that the dis- 

 credit into which this theory has fallen since 

 the days of Palmieri is due partly to a not 

 unnatural reaction from his somewhat extreme 

 views on the subject and partly to a misunder- 

 standing of the mode of action, the few at- 

 tempts which have been made to show a cor- 

 respondence between the lunar phases and 

 volcanic phenomena being rather inconclusive. 

 Ricco, in an inter^ting pamphlet,^ gives tables 

 showing, in four cases, a coincidence between 

 luni-solar combinations and the eruptions of 

 Stromboli, but neither the coincidence here 

 nor the lack of it in five remaining cases 

 seems very definite, because the time of the 

 eruptions is merely given as the "' date of the 

 beginning of the periods of singular activity." 

 External influence upon earthquakes has been 

 more generally studied, Schmidt having pre- 

 sented" a carefully prepared summary of the 

 effect of lunar distance, luni-solar positions, 



^ " Sulla influenza liini-solare nelle ernzioni, del 

 Prof. Riceo." 



= •■ Stud. ub. Vnllr. u. Erdbeben," Leipzig, ISSl. 



