The sun., 1894-11-11


difference between a refracting and rejecting
telescope IL wide, and for many years refractors
asvs enjoyed hs Of
source Of most Of the advances made in astroD
n2mical knowledge. refractor, like the
Lick o.. or the IeTkes, for example; has a
tube which refracts or bends all the rays OF
light from heavenly body which fall upon it.
end Of the tube where the magnifying lens or
eye piece Is tixed and gazed through 6y the OBJ
glass at the outer end, but a mirror ~ the most
perfect construction at the bottom, this mirror
reflects ali the light back To- the tube and Al.
rectly or indirectly focuses It at the eye piece as
before, the observer gazing at the reflected i'm
tractor and reflector have their special disad-
yantsges. the difficulty in the former being what
the difficulty, II not iinpossibilty. of bringing
all the different rays of light TO common
focus. and the great problem in refractor con-
struction is by improvement OF the glass used
TO do away with this alteration.
TO BE SUSPENDED IN WATER.
There is another difficulty, however. which.
with recent improvements In the reflector has
created new and great opportunity for the lat
ter. This is the demand OF astronomical pho
Biography for instruments Of larger and larger
photography require an exactness of adj djustment
and clockwork motion TO counteract the motion
same relative position to the object being pho
tographed, which is almost impossible to OBJ
weight now desired The great reec,oss "f tSs
future, however. will have no weight at all me-
Gihanicaily sPeaking because they will be iioated
In water. This strange and novel principle, due
20 the invention OF DR.. Common, Is Impossible in
the case OF refractOrs, because the observer
would necessarily be at the bottom OF the water,
but with reheCtors IL shows every promise OF
availability and enduring success. Consequently |
all the great reiectors of the future will prob
ably be tank telescopes and this departure ia |
perhaps the greatest novelty in telescope mount
Ing that has yet appeared.
SIR HOWARD GRUBB.
Sir Howard Grubb as a telescope max er ocnn-
pies the highest rank. His whole life has been |
devoted to the study OF telescopes and their |
among others the great Vienna teiescope4 The |
great Melbourne reflector, and many others OF |
lfss nc bGIng new Hsipch refractor for
Tor the same Observatory which he has in hand.
rervatOry, and as "a maker and an authority ON |
telescopes is the 1rst In Europe. He was the
Ing the Lick and the Yerkes, and his sdop-
PFfiH'' H. p4sctssSG srS full svdonsS
method il recent lecture at tie royal iSstita in iiS
ien; ;i9oI monster, estimates and designs S for for
Which he has been requested TO make from
ply, The great six foot reflector OF lord Rosss
Ness was always limited by the lack Of an "ss eaaa.
Orial mounting II was hung on chains ha
wega Ta tT% ~ % walls and Consequently covered only
an: N 1868 SIR Howard GTubb mounted equa-
orially the foyr-foot reflector at Melbourne,
! hve-fooi instrument Of this kind.
THE PROJECTED TES-FOoT REFLECTOR.
During a late visit to London Sir Howard con-
ented 70 be Interviewed, aud was seen at the
irand Hotel, lie is a young looking man, Of
middle age, with the quick thought and genial
manners oi an Irish gentleman, aud he is very
Ter o n laf a. IA Ggia l.
Medium height and slender build, hut his great
mental activity and rapid speech took his inter-
ties than he had ever expected 10 traverse In a |
ifetims. sir Howard, being asked as 10 the
/ have been asked Tor and have pre-
AIRED estimates and "A model Of that in
ects under discussion, but with these e'' I
Mount the instrument il desired. Il VIII VIII have ave
hickness Of the steel i'll be three-eighths Of an
loh, and the Two steel shells will be separated
y space Of three inches. The object Of this is
D equalize The temperature and avoid the mix
are and consequent movement Of the air at the
lOuth Of the tube. This movement would arise 1
rom the difference OF temperature between the !
IL inside and that outside, and would cause a
onsequ uent movement In the rays OF light To ,
rom the cavity between the shells, which 10 {
losed at the top and open at the bottom inside I
air passing down the tube and avoid the in
lTinus irregular mixture 4
much one hundred tons, though no weight a
i'll fall on the bearings. IL would probably bs 4
mechanical impOssiGility TO drive an instFu- | Z
Ient OF this weight by clOekwOTk. IL II were I
Ounted In the ord nary way, with the absolute I
eAdiness, smOOthness. and accuracy necessary [
II observing and, above all, for Photographic a
lTpuses. The only way OF getting rid OF the u
eight is the ingenious method Of ho!ation first )
lggested by DIR. Common, = principle which | | n
ave somewhat developed In the present in
ance. The steel tube carrying the reflector at /
e bottom will tnat IN a reservoir 100 feet In N
anleter and so or 80 feet deep. The tube will n
water tight OF course. c
" To appreciate the praetioabllity Of this 4
ethOd, you have only To take hollow tube, | /
AteF-tight az end. which expands In The | n
rm Of a sphere about tho middle OF tts upper ! "A
NJ By carefully constructing Il you can hOat ! n
az almost any angle of inclination, and ID will p
main In perfect equilibrium down To q certain | y
Fy small angle. The weight OF the tube, OF | n
urse, equals the weight Of the water which ID | Al
splAces. The greatest angle over which Il will iI
main IN perfect equilibTium depends upon the sb
rLn aof the tube, but with the Proportion | d,
stoss "a thS tube wiz Be dsPrssalbls q psrfsct q