654 



SCIENCE. 



[N. S. Vol. XI. No. 878. 



appears greatly flattened out in the other 

 one, and hence a maximum in one may cor- 

 respond to a minimum in the other. The 

 farther the stations are from each other, the 

 more frequent and clearer become the 

 differences between the curves, so that at 

 very distant points there are but few de- 

 tails which the curves have in common. 

 Especially characteristic of these fluctua- 

 tions of the earth's magnetism is the con- 

 tinual change controlling them ; remark- 

 able similarity is followed in a few minutes 

 by a pronounced dissimilarity — a violent 

 outbreak in the one curve corresponds to 

 an almost imperceptible bending of the 

 curve in the other. This well known 

 peculiarity in magnetic storms shows with- 

 out doubt that local influences are the prime 

 cause of the phenomena— occurrences of 

 rapidly changing strength and extent which 

 — now here— now there — make their pres- 

 ence strongly felt, and while the effect may 

 reach practically simultaneously over a 

 very extensive area, the maximum travels 

 rapidly from place to place. Dr. Schmidt 

 made a mathematical analysis of vari- 

 ous magnetic storms and in particular of 

 the one which occurred on February 28, 

 1896, and whose course was followed one 

 hour, from 6 to 7 p. m. Greenwich time, at 

 the suggestion of Professor Eschenhagen, 

 simultaneously by 15 observatories distrib- 

 uted over the earth. His investigations 

 clearly showed that the disturbance vectors 

 at times converged to a point, at other times 

 radiated from a point and, in times of mag-" 

 netic calms (comparatively speaking), the 

 vectors at the various stations were almost 

 parallel to each other as though pointing to 

 a distant force- center. Furthermore that 

 the points of convergence, in general, moved 

 progressively forward with a velocity of 

 about one kilometer in a second and also 

 that they were at times nearly stationary. 

 In view of the fact that the cause of the 

 diurnal variation of the earth's magnetism 



must apparently be referred to electric cur- 

 rents in the upper regions of the atmo- 

 sphere. Dr. Schmidt believes that the im- 

 mediate cause of the magnetic storms is to 

 be referred to electric whirls or vortices 

 which separate themselves from the general 

 electric field in the atmosphere just as do 

 the cyclones and anti-cj'clones known to 

 the meteorologists. Taking also into con- 

 sideration the vertical disturbing compo- 

 nents and applying Ampere's rule to the 

 current systems revealed by the disturb- 

 ing forces, it follows that, for the greater 

 part, the causes of our observed magnetic 

 storms come from outside of the earth's 

 crust. 



Professor Eschenhagen's recent work follows 

 naturally upon this brief statement of the 

 work of Dr. Schmidt, for it is largely due to 

 his energy and the instrumental methods he 

 has devised that Dr. Schmidt's investiga- 

 tions have been made possible. 



We shall have thrown, presently, upon the 

 screen a lantern slide showing the delicate 

 transportable variation instruments devised 

 by Eschenhagen. The results reached by 

 him with these instruments revealed the 

 desirability of again inaugurating a system 

 of simultaneous observations of the earth's 

 magnetic variations at various points, and 

 so was begun the scheme of observation 

 which furnished Dr. Schmidt with the neces- 

 sary material. Eschenhagen has likewise 

 made some very interesting investigations 

 as to the effect of Berlin electric tramways at 

 various distances, with the aid of his simple 

 set of variation instruments. 



You will see later on the screen curves 

 obtained by these instruments showing the 

 effect of the tramways at various distances. 

 If these small variation instruments prove 

 upon trial, covering a sufiiciently long period 

 to be satisfactory in every respect, their 

 small initial cost and also that of their main- 

 tenance will, without doubt, do much to- 

 wards increasing the number of stations. 



