Telescopes and other Reflecting Instruments.
Year: 1885

page_text: Telescopes and other Reflecting Instruments.
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I, Dr VOJTĚCH SXFXRIK, Professor of Chemistry in the Bohemian University
of Prague in the Impery of Austria, do hereby declare the nature of my Invention
for IMPROVEMENTS IN THE CONSTRUCTION OF METALLIC SPECULA FOR TELESCOPES
AND OTHER REFLECTING INSTRUMENTS to be as follows:
My invention consists in casting telescopic specula of a particularly hard and
tenacious bronze, composed of copper, tin, and phosphorous, with or without the
addition of zinc and with the addition of metals apt to augment its hardness as
well as the tenacity of the alloy, such as iron, manganese, nickel, cobalt, chronium
molybden, tungsten etc.-In grinding and polishing such alloys and then depositing
hydro electrically on the polished surface an exceedingly thin film of very white
inoxydizable metals such as silver, palladium, platinum etc.
Specula made in this manner combine the good qualities of the old metallic
specula, and of the modern silvered glass specula; they do not tarnish like the
former, and the reflecting film does not split off as in the latter. At the same
time they are much stronger and less brittle than both, and may be cast much
thinner than specula of Edwards or Rosse's alloy thus diminishing weight and
expense-Some of my improved alloys show three times the tenacity of best cast
iron.
A great advantage of my method consists in the possibility of turning these
alloys in the lathe, and thus very much reducing or quite avoiding the tedious
process of grinding by emery.

page_text: Telescopes and other Reflecting Instruments.
I, Dr VOJTĚCH SXFXRIK, Professor of Chemistry in the Bohemian University
of Prague, in the Empire of Austria, do hereby declare the nature of my said
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
My invention consists in the construction of specula of particular alloys; in
grinding them by particular methods; and in coating them with a film of highly
reflecting and inoxidable metals. These metallic specula being suitable for
reflecting telescopes, and other reflecting instruments.
The metallic specula now in use such as those of Edward's and Rosse's alloys
are excessively brittle, and liable to tarnish. They must necessarily be made
thick and heavy, and their optical efficiency is easily injured in repolishing them.
The silvered glass specula are also brittle, and the thin silver film does not adhere
sufficiently to make it durable. It is soon injured by repolishing shewing scratches
and pores which transmit the humidity of the air through the silver film to the
glass. This tends to split it off, so that from time to time a new film must be
deposited, which is a delicate chemical operation, not at all sure of success at all
times.
To avoid the inconvenience of both the metallic and the glass specula now in
use, I construct my specula of particular alloys, or specular bronzes, these being
prepared for this special purpose. The alloys contain 60 to 80 per cent of copper,
with 15 to 25 per cent of tin and 0.1 to 1.3 per cent of phosphorus. An addition
of nickel or cobalt (extending to 18 per cent), of zine (to about 10 per cent), and
of iron (to 2 per cent), as well as of manganese, chromium, molybdenum, tungsten
and antimony, augments the hardness as well as tenacity and reflecting power.
Because of the high price of some of the enumerated additional metals, and their
intractableness in uniting perfectly, with other metals, and to form an alloy
sufficiently homogeneous for the present purpose, I use for the construction of my
metallic specula, alloys of which the following five are the types:
Type A, with 75 per cent of copper, 24-8 per cent of tin and 0.2 per cent of
phosphorus. The transverse strength of this alloy is 21 kilogrammes on a
square millimetre.
Type B, with 75 per cent of copper, 23-75 per cent of tin and 1.25 per cent of
phosphorus. The transverse strength of this alloy is 40 kilogrammes on
a square
illimetre.
'
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Type C, with 682 per cent of copper, 25°4 per cent of tin, 5.1 per cent of nickel,
and 13 per cent of phosphorus. The transverse strength of this alloy
is about 50 kilogrammes on a square millimetre.
Type D, with 744 per cent of copper, 21.9 per cent of tin, 2.5 per cent of zinc,
and 12 per cent of phosphorus. The transverse strength of this alloy is
27 kilogrammes on a square millimetre, and
Type E, with 69 per cent of copper, 201 per cent of tin, 8.9 per cent of zinc,
1.9 per cent of iron, and 0.1 per cent of phosphorus. The transverse
strength of this alloy is 29 kilogrammes on a square millimetre,

page_text: The indicated transverse strength is obtained without pressure, in casting the
alloys in an iron ring placed on a flat bed of compressed iron ribbons. No special
annealing of the disc is required. By special arrangements the transverse strength
can be increased, if necessary.
Rosse's
All these alloys are brilliant, homogeneous and dense, pale yellowish, and can be
turned on the lathe. Types A and B are nearly equal in hardness to Rosse's metal.
The other types are less hard, but still sufficient for the present purpose.
metal possessing a transverse strength of only 9 kilogrammes per square milli-
metre, i.e. from three to six times less than my alloys. My specula can be cast
much thinner than usual, and they are therefore considerably lighter and cheaper.
A 4 inch speculum of my alloys is difficult to break by blows of a small hammer,
while one of Rosse's alloy cracks if struck with a key.
My alloys as given above, are less white and less reflecting, and more subject to
tarnish than Edward's and Rosse's. If used alone, they would not be so good as
those. The immense advantages of a reflecting surface of noble metals are secured
to specula made of my alloys, by coating them hydro-electrically, after they have
been polished, with a very thin film of any white inoxidable metal, such as silver,
palladium, platinum, iridium, rhodium, and others of that class.
This method offers the following advantages:
:
(1) It imparts to my alloys the high reflecting power and perfect whiteness of
silver or the other noble metals aforesaid.
(2) It protects the alloy from oxidation, and makes specula of this kind in-
alterable, and far more durable than those of the old kind.
(3) My specula, if tarnished, can be repolished in few minutes like silver-on-
glass specula, with a soft leather-pad and some fine rouge; without altering their
figure and optical efficiency.
(4) In consequence of the strong attraction between metal and metal, the silver
film never splits off, and fine scratches if produced by repolishing are of no other
consequence, than the slight diffraction of light which they cause.
Taking the reflecting power for white light of Rosse's alloy = 0·66 and of
silver = 0.91, the proportion is = 0.725: 1 or = 1: 1.379, and the proportion of
the square roots of these numbers
0851:1 or 1: 1.174, i.e. a silver speculum
of 10 inches will give the same light, as an 11-74 inches one of Rosse's alloy, or
an 8.5 inches silver speculum will be equal to one of 10 inches of Rosse's..
=
Platinum and palladium possess a reflecting power inferior to that of silver for
visual rays, but superior for chemical rays, and, for astrophotography, platinized
specula may give a distinct advantage. By a weak current and a very diluted
silver bath (about 1 per cent of silver) it is easy to produce on my polished specular
bronzes, brilliant silver films, requiring very little leather polishing; platinum, on
the contrary, is difficult to deposit as a specula layer on bronze. I could obtain
brilliant platinum films only after previously giving a thin silver coating.
In the usual process of grinding, a disc of speculum metal, roughly cast to the
required curvature, is shaped to its exact figure by rubbing it in every direction
on a convex iron tool, with interposition of a thin paste of water and emery,
increasing by degrees of fineness, till a smooth exactly spherical, surface is
produced, which is ground on a convex slab of stone or slate. The grinding by
emery is very tedious, and leaves the surface very rough; for the freely rolling
grains of emery act as chisels and splinter off the brittle unyielding metal in small
fragments. My alloys, being a little softer and more yielding than Rosse's, are
first turned in the lathe to the required curvature. Then they are ground on dry
convex emery wheels of the proper curvature, by hand or in the lathe until all
traces of turning disappear. The abraded metallic powder is brushed off at
intervals. With specula of moderate dimensions it suffices to glue a sheet of
emery paper or cloth on a convex slate disc finely ground to the required
curvature. Two different emery wheels, one coarse and the other fine, have to be
used. This process is very much shorter than the old one, and leaves the speculum

page_text: very smooth and lustrous, so that the stone may be immediately applied. The
reason of this is:-
(1) That the grains of emery cannot roll freely in every direction, but only
in the direction of the stroke.
(2) That the grains of emery being fixed, cannot enter so deeply into the metal,
but act only by scraping it superficially, like a file.
j
The materials and methods described above are applicable to all kinds of
metallic reflectors, curvilinear and plane and my methods are applicable to all of
them.
The advantages of my specula in comparison with Rosse's increase by casting
them thinner, but with deep crossed ribs on their backs Lord Rosse's 6 feet
speculum has equal light with a silvered one of 61.3 inches. The first will weigh
80 cwt whilst mine of equal optical power will only weigh 20 cwt. The casting
with ribs is not feasible with such an intractable material as Rosse's, but quite
easy with my highly fusible and tenacious specular bronzes.
Having now particularly described and ascertained the nature of my said
Invention, and in what manner the same is to be performed, I declare that
what I claim is :-
:
1. The manufacture and use of metallic specula formed with improved alloys
whereby lightness and strength are secured, substantially as and for the purposes
herein before described.
2. The improved method of forming spherical specula by turning the same in a
lathe and polishing with emery wheels, substantially as and for the purposes
herein before described.
3. The improved method of depositing upon specula thin metallic films of
inoxidable noble metals, and thereby augmenting their optical power and
durability, substantially as and for the purposes herein before described.
4. The general construction arrangement and combination of the several metals
and alloys, and the methods of using and working the same, together forming my
improvements in the construction of metallic specula for telescopes and other
reflecting instruments, substantially as herein before described.
Dan h Ammil 1000