SCIE^'TIFIC SUMMAKT. 
107 
was manifest. The spectroscope (pocket, by Hawkins and Wales) was first 
turned on the full moon, and an idea of the length of the spectrum obtained 5 
then with a wide slit it was turned on the aurora, and the following sketch 
made, which was carefully verified, so that it represents exactly what I saw. 
The Tiolet (extreme) rays seemed cut off j and I saw 1st, a broad and bright 
red band ; 2nd, a black space equal in width to it ; 3rd, 'a green and bright 
band nearly as wide ; then a faint spectrum of diffused light, and a bright 
line in the blue j then a bright line more refrangible, but whose colour could 
not be definitely seen. I then opened Angstrom’s Spectre Normal,” and 
saw that he gave the auroral line as in the' yellow. I observed this green 
line again, and cannot persuade myself that it was yellow. The black space 
I am sure of; and it was also seen plainly by an inexperienced person, into 
whose hands 1 put the instrument. - The slit was then narrowed and turned 
on the moon, and adjusted to give the Fraunhofer lines most clearly. The 
aurora by this time was fainter, and I can only be sure of a bright line 
(green), with a suspicion of my former blue line. Opening the slit again, 
the red band of the diffused light spectrum was dose against the green bright 
line. The aurora then faded. I mention this black space, as it is not what 
I expected to see from my reading of Angstrom and Winlock. 
The Physics of a Fog . — At the meeting of the Manchester Philosophical 
Society October 29, 1872, Dr. R. Angus Smith, F.R.S., described a remark- 
able fog which he saw in Iceland. It appeared to rise from a small lake 
and from the sea at about the same time, when it rolled from both places, 
and the two streams met in the town of Reykjavik. It had the appearance 
of dust, and was called dust by some persons there at first sight. This arose 
from the great size of the particles of which it was composed. They were 
believed to be from to of an inch in diameter. They did not show 
any signs of being vesicular, but through a small magnifier looked like 
transparent concrete globules of water. They were continually tending 
downwards, and their place was supplied by others that rolled over. 
Currents o~f Flectricity in Plants . — Some curious experiments have been 
recently made on this subject by Herr Dr. Ranke, who has published his re- 
sults at considerable length, in the Sitzungsbericht ” of the Bavarian 
Academy. Among other remarkable facts noticed by the author, was the 
fact that, as in the electricity of animals, the electromotive action was ob- 
served where the fibres did not lie parallel to the longitudinal axis. The 
pieces experimented with, then, were cylindrical pieces from the petioles of 
the Rheum undulatum, their longitudinal axis corresponding with the axis 
of the petiole, and they were terminated by two cross sections perpendicular 
to this axis. They were two to three c.m. in length, and 0'5 to 1’5 c.m. 
diameter of section. The apparatus for measuring the currents wms similar 
to that used by Du Bois Reymond in his experiments. If a piece of the 
kind described wap taken, and one electrode applied to the cross section, the 
other to any point of the uncut epidermis, the false current appeared, the 
cross section being negative to the other surface. If now the outer surface 
of the piece was removed by cutting parallel to the axis, and the electrodes 
were applied, one to the cross section, the other to the surface laid bare as 
described, there was in every case a current observed, the direction of which 
was from the surface of cross section to the other (through the wire) ; hence 
