444 
NATURE 
[ Feb. 24, 1870 
are appropriated to the polishing machine, crane, and engine ; 
the remaining 28 feet are divided into two rooms, one of which 
is at present used as an office, the other, 25 by 14, is intended 
for a laboratory. The moyeable roof is 40 fect long, and runs 
on rails laid the whole length of the walls; the telescope room 
may therefore be completely covered in, and as completely un- 
covered when required, the roof in the latter case resting on the 
south building, which on that account has a very low permanent 
roof. The telescope, when housed, lies meridionally on the east 
side of the pier, and nearly in a horizontal direction, provision 
having been made to prevent the tube being lowered beyond a 
certain small inclination. Some trouble was experienced in re- 
moying the varnish from the specula, and they would require 
repolishing. Of work done, the author could not yet speak 
with any satisfaction since it became at all practicable to 
use the telescope ; the history which he had to relate was a long 
chapter of weary heart-breaking watchings, with an occasional 
half hour’s work. 7 Argis was the first object observed for pur- 
pose of delineation ; after the first night’s work little (and that 
by snatches) was done towards it; a new inroad of workmen 
and a long course of extremely unfavourable weather having 
carried the nebula out of convenient reach. The search, which 
was reluctantly given up, will, however, be again soon resumed. 
The horseshoe nebula is a grand object, conspicuous and with 
shape even in the finder. It appears, however, to present no 
marked difference (with perhaps one exception) which may not 
be accounted for by the difference of aperture used. This excep- 
tion is the presence of a small but conspicuous double star at the 
s p angle of the knot which lies between the g and the bright 
streak ; the experiment has not been tried of cutting down the 
aperture to approximate to an 18-inch Herschelian, but the 
intrinsic brightness of the principal star, and the presence in the 
C GH of stars not more bright (No. 3 of Herschel’s catalogue 
is certainly less bright) go far to show, without this experiment, 
that the star did not exist as such with its present brilliancy at 
the time of the C G H and P T 33 observations. The impor- 
tant position of the star, and the careful scrutiny which the knot 
and its neighbourhood must have repeatedly ‘undergone, forbid 
the assumption that it was simply overlooked by Sir John Herschel. 
The star 6 is conspicuously and beautifully double, the com- 
panion of considerable brilliancy, about 15 mag. ; with its pre- 
sent brilliancy and elongation, the author thinks, it should be 
within reach of an 18-inch. The appearance of the knot is 
sparkling, though no discrete stars can be seen, except perhaps 
a second faint one, which is suspected at thes f angle; part of 
the streak near to the knot isalso sparkling, but not in so marked 
amanner; the other portions appear of the ordinary milky nebu- 
losity. The fainter nebulosity (S) of the bright streak pretty 
well marks out the borders of the almost vacuous lane which 
leads up to and past the knot ; on receding from the lane it be- 
comes very faint ; nor is this faintness uniform, but the appear- 
ances are so fugitive that, after repeated and painful effort, they 
could not be caught. The borders, however, stretching to the 
stars are occasionally pretty well seen. On one or two occasions 
the author suspected the existence of a link between the nebu- 
losity about the star No. 10 and the lower portion of the %& ; this, 
however, requires verification. At the f end, the upper 
and smaller semicircle is plainly marked, the lower and 
larger very faintly; its exact figure is, therefore, uncertain. 
3570 is a small but beautiful spiral. The two brighter knots 
are resolvable. Of work out of the regular course, amongst 
other things, Neptune has been observed on some five or six 
occasions for figure and a second satellite, with only negative 
results. In the absence of a photographic apparatus to be used 
at the uninterrupted focus of large mirror, attempts have been 
made to utilise the second or Cassegrain image ; an average ex- 
posure of near ten minutes on an eight-day moon produced 
pictures which (by no means good) were of sufficient promise 
to make it worth while to resume the attempt under more 
favourable conditions. The time of exposure is somewhat sur- 
prising, and would seem to indicate a great loss of chemical 
rays by a second perpendicular reflexion; but perhaps the 
inactivity was mainly due to absorption at the surface 
of the large mirror, which was then very yellow. The 
spectroscope arrived some time ago, but has not been much 
used ; it is thought that for stax work of any value some modifi- 
cation will be required, principally the exchange of the present 
collimator for one of longer focal length ; a greater dispersion, 
moreover, seems desirable. The spectroscope was mainly de- 
signed for. nebula work, is handy and compact, and will be 
of much service. For spectroscopic work on objects haying a 
sensible diameter, the great telescope itself labours under some 
disadvantages ; the enormous focal length and consequent mag- 
nification of the image is a serious inconvenience in the case of 
faint objects, and may be only partially remedied by a suitable 
condenser. This magnifying of the image may, however, in 
some cases be advantageous, from the possibility thereby 
afforded of viewing small definite portions of moderately bright 
objects, though unfortunately that will be seldom. Of nebule, 
Orion has been examined for purpose of practice; the three 
lines are plainly and conspicuously seen ; the hydrogen line is 
comparatively much fainter than was anticipated, disappearing 
in the fainter portions of the nebula. 30 Doradis shows the 
nitrogen line with facility, the second line certainly, but not in 
all positions, and always with difficulty ; the hydrogen line is 
suspected only. No trace of a continuous spectrum could be seen. 
7 Argis has been observed on only one unfavourable morning ; the 
nitrogen line was seen over a considerable space ; the presence or 
absence of others, or of a continuous spectrum, could not be stated 
with certainty. With respect to future operations, it is intended that 
at first the routine work shall consist of a detailed delineation of the 
objects figured by Sir John Herschel, or any others which may 
prove interesting ; this will take some time; for even without 
the impediment of cloudy weather, the delineation with any 
degree of satisfactory correctness, of a moderately large nebula, 
requires a considerable amount of work with careful and frequent 
scrutiny. It is hoped, however, that this work will by practice 
be found less painfully difficult than it is at present. The 
spectroscope will be used as much as possible, the moon photo- 
graphed, and attempts made to photograph the nebulee, when a 
photographic apparatus has beenpr ocured, and staging, photo- 
graphic room, &c., added to the building. It is moreover hoped 
that before long a refractor, of some nine inches aperture, may 
be procured, to be mounted with the reflector, or, preferably, as 
a separate instrument. ‘This telescope, besides being of much 
general use, will find much and valuable employment in 
determining micromctrically the chief points in the nebule 
under examination with the reflector, with more expedition and 
accuracy than at present; for spectroscopic work this telescope 
would be a valuable adjunct, especially if it be constructed of 
such comparatively short focal length as seems now to be 
practicable. 
“On a distinct form of Transient Hemiopsia,” by Hubert 
Airy. From a comparison of the different accounts of ‘‘ Hemi- 
opsia,” ‘* Half-vision,” or “ Half-blindness,” by Wollaston, M. 
Arago, Brewster, the Astronomer Royal, Dufour, Sir John Her- 
schel, Sir Charles Wheatstone, and Mr. Tyrrell, the author con- 
siders that, irrespective of the wide primary distinction between 
the transient and permanent forms of Hemiopsia, there are 
different forms of transient Hemiopsia which haye all been in- 
cluded under the same name; Wollaston, Arago, Brewster, and 
Tyrrell, describing one form of the transient affection, while Sir 
John Herschel, Sir Charles Wheatstone, the Astronomer Royal, 
Professor Dufour, and the author agree in describing another. 
As to the actual seat of the visual derangement, the author con- 
siders that the exact agreement of the two eyes in the nature, 
extent, and degree of their affection, proves (assuming the semi- 
decussation of the optic nerves at the chiasma) theseat of the affec- 
tion to be at some point behind the chiasma of these nerves. All 
the causes that are found to lead to transient half-blindness, 
point to the brain as the seat of disturbance. Still clearer is 
the evidence given by the loss of speech and of memory, the 
derangement of hearing, and the partial paralysis which some- 
times follow an attack of teichopsia. Such cases as Sir John 
Herschel’s, where the cloud passed over the whole field from 
left to right, can only be explained by supposing the disturbance 
to lie in some region of the brain where the opposite halves are 
in contact. The mischief may possibly be seated in the corpora 
quadrigemina or geniculata, or even in the cerebellum itself. The 
phenomena are so definite and so localised, and their course is 
so regular, that we can hardly avoid the conviction that their 
cause is equally definite and equally localised ; and it is difficult 
to admit so vague an agent as nervous sympathy with gastric de- 
rangement, except as acting through the medium of some 
secondary local manifestation in the brain. 
Chemical Society, February 17.—Prof. Williamson, F°. R.S., 
president, in the chair. The following gentlemen were elected 
fellows :—R. T. Atcherley, T. W. Axe, A. H. Bateman, 
E. Francis, A. Prangley, W. Pritchard, L. B. Ross, T. G. 
