380 
conception and inexperienced personnel, will 
do good work, we have no doubt; for it is the 
saving grace of our American navy, that its 
officers are apt in utilizing brief experience, 
fertile in expedients, and bold in execution of 
a task before them. 
THE GREAT VIENNA TELESCOPE. 
AmoneG the instruments which I have exam- 
ined, that to which most interest now attaches 
is the great telescope recently completed for 
the Imperial observatory at Vienna by Howard 
Grubb of Dublin. It is the largest refracting 
telescope in actual use at the present time, being 
of one inch greater aperture than that of the 
Naval observatory at Washington. The con- 
tract was made with Mr. Grubb in 1875; but, 
owing to difficulties in procuring glass disks 
of the necessary size and purity, it was not 
completed until1881. Further delays occurred 
in mounting, so that it was scarcely ready for 
actual work at the time of my visit in April 
last. I made as critical and careful examina- 
tion of its working as was possible during the 
unfavorable weather which prevailed at Vienna 
at that time. My examination was principally 
in the nature of a comparison of its working 
with that of the Washington telescope. 
General character of mounting. —In_ its 
main features the telescope is mounted on the 
same general principle with that at Washing- 
ton. Both of these instruments are counter- 
poised on the German plan. The tubes of 
both are of steel. The rapid motion in decli- 
nation is by means of a rope attached to the 
two ends of the tube, and that in right ascen- 
sion by a system of wheel-work. The clock- 
work is in the pier below the instrument. The 
leading points of difference are, that the mount- 
ing of the Vienna telescope is much larger, 
stronger, and heavier in all its parts; that the 
contrivances for making use of it are more 
numerous ; that an elaborate system of fric- 
tion-rollers in declination is provided, the 
Washington telescope having none; and that 
i more convenient system of illuminating the 
field and the divisions on the several circles 
has been adopted. 
Ease of motion. —In moving the Vienna 
telescope, one is at first struck with the fact 
that mere weight is a serious drawback ; but 
when the motion is once commenced, the moye- 
ment in right ascension is almost as easy as 
in the Washington telescope. It is, however, 
_ 1 Extract from a report to the secretary of the navy on recent 
improvements in astronomical instruments, by Simon NEwW- 
COMB. 
SCIENCE. 
[Vor TIL, No. 60. 
very different in declination. For reasons 
which neither Dr. Weiss nor myself were able 
to perceive, the friction-rollers seemed to be of 
no benefit in easing the motion in declination, 
which was much more difficult than in the 
Washington telescope, and, in fact, quite a® 
task upon the strength of the observer at the 
eye-piece. The quick motion for setting in 
right ascension is made below the end of the 
polar axis by turning a steel steering-wheel. 
This appliance is in every way inferior to the 
system at Washington, where the same motion 
is effected by an endless rope hung over a 
grooved wheel, which the observer turns hand 
over hand. By this motion the observer at 
the Washington telescope can make the re- 
quired motion without taking his eyes from the 
telescope or the vernier, and without giving 
any thought to the motion of his hands. But 
the handles of the steering-wheel are much 
less convenient to take hold of than a rope; 
and, if the motion is at all rapid, the operator 
must be on the alert lest the steel handles 
strike his knuckles in the attempt to take hold 
of them without looking. The necessity of 
care in this respect makes the motion slow and 
laborious. 
Clock-motion. —On the system of the Messrs. 
Clark, applied in the Washington telescope, the 
screw which turns the sector does not take hold 
of the circumference of the latter directly, but 
gears into a complete wheel, the axis of which 
is connected with the arc of the sector by a 
pair of brass or steel bands. By this arrange- 
ment the toothed wheel makes a nearly com- 
plete revolution while the sector is moving 
through its arc; and the effect of the small 
unavoidable irregularities in the working of the 
screw is diminished in the ratio of the are of 
the sector to the circumference of the wheel. 
Whatever advantages this arrangement may 
have in small instruments, I think that in large 
ones they are more than counterbalanced by 
the evils arising from the elasticity of the band, 
combined with the changes of friction, the 
action of the wind, and other forces acting 
to vary the uniform motion of the telescope. 
Owing to this elasticity, the effect of the wind - 
or of any slight pressure by the observer on — 
the eye-piece is many times greater in the 
Washington than in the Vienna instrument. 
But it did not appear to me that the firmness 
of the connection in the latter instrument be- 
tween the support of the turning-screw and the 
tube of the telescope was as great as supposed 
by those who lay stress on large and stable 
mountings. I found that, by a simple pressure 
of the thumb-nail upon the eye-piece of the 
