48 Perret — Representation of Volcanic Phenomena. 



Art. III. — The Diagrammatic Representation of Yolcanic 

 Phenomena j by Frank A. Perret. With Plates I to IV. 



As an aid to comprehension in the presentation of a subject 

 the visual sense is now appealed to in a constantly increasing 

 degree and a description without illustrations, a report without 

 a drawing, or a lecture without projections has become almost 

 an exception. Exquisitely sensitive to infinitesimal variations 

 of form and of angle, the eye is capable of conveying to the 

 mind, not only the reproduction of a scene, but even the 

 summed-up impression of a series of measurements, or the net 

 results of a laborious analysis, as presented in a diagram or 

 curve. And, in such a case, it is precisely this property of 

 totalizing, so to speak, — of eliminating distracting intervals 

 and showing, almost at a glance, those collected values which 

 must otherwise have been considered one by one — which 

 constitutes the principal advantage of this method, and gives 

 to it the quality of being at once analytic and synthetic. We 

 may see, therefore, the gradual cooling down of a molten mass 

 plotted out in the form of a curve, of which beginning, pro- 

 gression and end are visible and comparable ; the details of 

 plant growth analyzed and totalized in a diagram ; the composi- 

 tion of rocks exhibited for comparison in a series of geometri- 

 cal designs. But it would be superfluous to insist further 

 upon the value of the principle — it is a theorem not needing 

 demonstration. 



Can a diagrammatic method be devised for presenting the 

 characteristics of volcanic action '? 



It may be said, first of all, that the process of photographic 

 illustration has already rendered immense service to this branch 

 of science whose phenomena are unfamiliar to the mass of 

 mankind and are of a grandeur and beauty which baffle 

 description. The earlier sketches were often but caricatures, 

 in many instances reducing the average volcanic cone to the 

 apparent dimensions — and almost to the angles — of a church 

 steeple, and it is by photography alone that the reality can be 

 adequately portrayed and thus conserved as a precious docu- 

 ment for all time. 



But even this process is circumscribed and limited in its 

 practical application, not merely by the frequent elimination 

 of the sine qua non by clouds of erupted material but also by 

 reason of the fact that a large proportion of volcanic mani- 

 festations are invisible and, finally, because the photographic 

 record is fragmentary and lacking in the above-mentioned ele- 

 ment of totality. It is evident, therefore, that a further means 



