TRANSACTIONS OF THE SECTIONS. 17 
and with an eye-hole at one end; a mirror turned on an axis at right angles to the 
tube ; and, in front of the mirror, a slip was cut away from the side of the tube, and 
the lens was inserted athwart the cut-out part. Part of the lens projected within the 
tube, and part outside of it and in front of the mirror. The screen was placed at 
the further end of the cut-out part, and an envelope protected the whole from injury. 
A slide in front of the lens regulated the amount of light thrown on it, and toned 
the image to the required degree of brightness. The addition of a telescope was not 
found practically of much use; neither was that of a second mirror, for double 
reflexion, to meet the difficulty of sending signals when the sun was behind the 
back of the signaller. It is not difficult to signal within 12° of the point opposite 
to the sun, and it is possible to do so within 7°. The looking-glass should be of 
the very best plate-glass, and it ought to have its sides truly parallel, else there will 
be a confusion of images and an irregularity in the flash. Letters are conveyed by 
treble groups of flashes, each of which groups consists of one, two, or three flashes, 
as the case may be. 
The author detailed the experiments he had made with the help of an assistant, 
and trusted that a full trial of the instrument at sea would be made by the authorities 
of the Navy, with a view of determining whether it should not be accepted by them 
as a subsidiary signalling instrument throughout Her Majesty’s Service. One of the 
land heliostats has been sent to the United Service Institution, in Whitehall Place, 
together with a more detailed explanation. 
On the Fixed Lines of the Solar Spectrum. 
4 By J. H. Guapstone, Ph.D., F.R.S. 
The author exhibited maps of the fixed lines and bands seen in the solar spectrum 
between those usually designated A and B, and of those which he succeeded in seeing 
beyond K. The light examined was that of the full sun at noon about midsummer- 
day. The dark lines and bands in the lavender rays coincided with those drawn by 
Prof. Stokes, as occurring in fluorescent phenomena; and with those of M. Becquerel, 
which occur in the photographic image; but the author’s map contained many finer 
ones. It extended to M. Becquerel’s N. Another map was exhibited of the dark 
lines and bands that make their appearance in the orange and yellow rays when the 
sun is near the horizon, as previously described by Sir David Brewster. The long 
space of air traversed by the sun’s rays when setting also absorbs the more refrangible 
rays, but makes no difference in the angular position of the fixed lines themselves. 
The light of the moon exhibits the same black lines, and, when close to the horizon, 
it shows the additional lines in the orange in the same angular position. The light 
of the moon, answering in position to the violet rays of the sun, appears lavender, 
and even grey, like the most refracted rays of the sun. As to the origin of these 
lines, Dr. Gladstone had endeavoured to determine whether they were due to the 
absorbent power of the earth’s atmosphere, as the lines in the orange appear to be. 
Fraunhofer’s conclusion, that they do not occur in the light of some of the fixed 
stars, was thought to be open to objection ; but the author’s observations on the light 
of the stars had not led him as yet either to a positive or negative result. Artificial 
lights seen at a very great distance might determine the point. If these fixed lines 
are dependent on the sun’s atmosphere, they ought to be darkest in the light coming 
from the edge of the sun’s disc; but the author had been unable to find any differ- 
ence between rays proceeding from different parts. 
On the Influence of Light on Polarized Electrodes. 
By W. R. Grove, M.A. F.RS. &c. 
The author, soon after the publication of Daguerre’s experiments, had shown that 
when light is allowed to impinge on a prepared daguerreotype plate in water, a vol- 
taic current is evolved which affects the galvanometer. In the present experiments, 
two platinized platinum plates are placed in dilute acid, and the one exposed to sun- 
light while the other is in the dark. A current is detected by a galvanometer con- 
nected with the plates, which, after many experiments, the author found was depend- 
ent upon the original polarization or unequal chemical action on the electrolyte, 
2 
