592 EEPORT— 1887. 



station without any trouble to us. The War Department detailed an officer of 

 Engineers — Captain Witkowski — who with his orderly preceded us to our station, 

 made all needed arrangements there, and made all the desirable observations for the 

 determination of accurate time. To him we are under the greatest obligations. 



Observations of the Eclipse. — The weather was cloudy during the whole time 

 except for a few moments about half an hour after the totality, when for a minute 

 or two the disc of the sun, partly covered by the moon, was visible between and 

 through the clouds. Of course all spectroscopic and photographic observations 

 were rendere<l entirely impossible. 



We hoped to be able to determine the duration of totality with some accuracy 

 notwithstanding the clouds, but it was found impossible to iix the moment when 

 totality began nearer than ten seconds or so, the diminution of the light having 

 been unexpectedly gradual. The end of totality, on the other hand, was much 

 more sharply marked, the observations of Captain Witkowski, Professor McNeill, 

 and myself all agreeing within a single second. 



The darkness, also, was far less intense than had been expected. It was possible 

 to read fine print even when it was darkest, and I noticed that the sash-bars in the 

 window of a building some 400 or 500 feet away remained discernible through the 

 whole totality. 



2. Observations of Atmospheric Electricity. By Professor Leonti Wbbek. 



I will try to give a short report of some experiments I have made during the last 

 year with regard to atmospheric electricity. It was formerly uncertain whether the 

 electrostatic potential would increase on going from the surface of the earth to 

 more elevated regions of the atmosphere or not ; whether the potential in a normal 

 (i.e., cloudless) state of the atmosphere was always positive or sometimes negative. 

 Sir William Thomson was the first to show, by exact methods of measurement, 

 that the increase of the potential with the elevation is very important, and 

 amounts to about 100 volts per metre. Afterwards the fact was proved by many 

 other observers, especially lately by Mr. F. Exner at Vienna, who found an increase 

 of sixty to six hundred volts per metre. These observations were made by means 

 of an electrometer. In consequence of many incon^ eniences which are connected 

 with the use of an electrometer, I have tried the measurements with a very sen- 

 sitive galvanometer. In this case it is necessary to apply an aspirating or exhaust- 

 ing apparatus — for example, a flame or a system of points — to the upper end of the 

 conductor, which is elevated in tlie atmosphere. In order to get a constant appa- 

 ratus I have u.sed 400 of the finest needles inserted in a metallic ribbon. This 

 system I have raised in air by means of a captive balloon, or by a kite which was 

 attached to a conducting string, or to a twisted line of the finest steel wire. In 

 this way the greatest height to which I have raised the points has been one to 

 three hundred metres. When the lower end of the kite line was communicating 

 with a galvanometer whose other pole was in contact with the earth, a cm-rent 

 passed through the galvanometer. For determining the strength of this current I 

 propose to call mikro-milliampere the 10-^ part of an ampere. At the height of 

 100 metres, in the average, the current begins to be regular, and increases to 

 4,000 or 5,000 of those units until the height of 300 metres is reached. The 

 increase is very regular, and seems to be a linear function of the height. I have 

 nevertheless found that the smallest quantities of dust contained in the atmo- 

 sphere, or the lightest veil of cirrus, disturbed the measurements very materially, 

 and generally made the potential lower or negative. Experiments of this nature I 

 have made at Breslau and at the top of the Schneekoppe in the ' Riesengebirge.' 

 Especially at the last station an increase of potential was observed, not only by 

 reason of the perpendicular height, but also by reaching such regions of the atmo- 

 .fphere as were situated horizontally to about 200 metres from the outmost steep 

 top of the Schneekoppe. 



Therefore it must, according to Mr. Exner, be assumed that the surface of the 

 earth represents a surface of equal potential, and that the consecutive surfaces of 

 higher potential are stretched parallel over the plane countries of the earth and 



