324 REPORT— 1893. 



At Wilhelmshaven, where from other reasons one might have expected 

 a larger motion, the latter is really comparatively small. Two very dis- 

 tinct waves present themselves in the diagrams, both causing maximum 

 excursions to the east on April 30 and on August 14. But on the average 

 the mean position of the pendulum remained pretty constant. This fact 

 is of some importance, considering that the column at Wilhelmshaven 

 had also been constructed five months before the commencement of the 

 observations, and that the heavy moisture of the cellar would in that case 

 csrtainly retard the process of drying. Thus it is not likely that the 

 strong motion which took place at Potsdam during the first month ought 

 to be ascribed to this cause. 



This conclusion would, however, not be justified in the third case, for 

 when observing at Puerto Orotava circumstances did not permit me to 

 lose so much time. If the considerable inclination of the column towards 

 the west during the first month be ascribed to the drying process, the 

 general motion of the zero-point is of a very simple form, and may be 

 explained by a slow tilt towards the east. 



It is only natural to suppose that all modern geological changes in the 

 island of Tenerifie emanate from the Peak as a centre. If this is true, the 

 observed tilt might be the consequence of a slow elevation of the island, 

 which would gradually increase the slope of the lower jiarts of the 

 mountain, and would find an end when the internal forces should again 

 succeed in breaking themselves a way through one of the weaker parts of 

 its flanks. 



When considering the interest which is attached to the Canary Islands 

 and the Pico de Teyde, especially in the history of volcanic theories, the 

 foregoing remarks, though only founded on a short series of observations, 

 will suflBce to indicate the service which might be rendered to geological 

 science by observing two horizontal pendulums during a sufficiently long 

 interval of time on opposite sides of the mountain cone. Places like 

 Icod de los Vinos, on the north side of the island, and Guimar, on the 

 south side, are probably to be recommended most, for not only do they offer 

 the comfort which is desii-able for a longer sojourn, but the surrounding 

 country is so full of interest as to form a most magnificent object for 

 scientific study of the most varied kind. 



IV. Seismological Phenomena and Others. — Some time before writing 

 this account I drew up a paper containing all observations on seismo- 

 logical phenomena obtained by myself, and lately by Professor Kortazzi at 

 Nicolaiew, up to May 1893. This paper is not yet printed, but will soon 

 be published in ' Petermann's Mittheilungen.' ' As it is impossible to enter 

 much into details here, I must refer the reader to this paper. Respecting 

 the phenomena of earth pulsations and other remarkable movements of 

 the earth's surface I am in a similar position, for another paper on these, 

 which is illustrated by figures representing some of the most curious 

 portions of the photographs, is about to be published in the ' Astronomische 

 Nachrichten.' ^ In order to avoid repetition I shall in the following re- 

 marks include all that may as yet be said about the later observations at 

 Strassbnrar, as far as it refers to the obiect of this section. 



The horizontal pendulum, besides constantly indicating the position 

 of the plumb-line in relation to the surrounding objects on the earth's sur- 

 face, affords an excellent means of controlling the momentary state of the 



' See list of papers, p. 309, No. 15, " See list of papers, No. 14. 



