AN IMPROVED PRISM FOR SPECTROSCOPIC AND OTHER PURPOSES
Year: 1875

page_text: LETTERS PATENT to Joseph Beck, of Cornhill, in the City of
London, for the Invention of "AN IMPROVED PRISM FOR SPECTROSCOPIC
AND OTHER PURPOSES."-A communication from abroad by Messieurs
James W. Queen and Company, of the City, County, and State of
New York, in the United States of America.
Sealed the 13th April 1875, and dated the 25th February 1875.
PROVISIONAL SPECIFICATION left by the said Joseph Beck at the
Office of the Commissioners of Patents, with his Petition, on the
25th February 1875.
I, JOSEPH BECK, of Cornhill, in the City of London, do hereby
declare the nature of the said Invention for "AN IMPROVED PRISM FOR
SPECTROSCOPIC AND OTHER PURPOSES," a communication to me from abroad
by Messieurs James W. Queen and Company, of the City, County,
and State of New York, in the United States of America, to be as
follows:-
T
11

page_text: glass or other transparent substance, in such a manner that the incident
ray and the mean ray of the emergent pencil shall be in the same right
line, that is, the action of the prism is direct, giving obvious advantages
over the common form.
The following is a description of the construction of the hollow
bisulphide of carbon prism, and will apply also to the construction of
solid glass prisms in cases in which the index of refraction does not vary
materially from that of bisulphide of carbon. It consists of a prismatic
framework of iron, brass, or other material having nearly the following
angles, namely, sixty degrees, thirty degrees, and ninety degrees. The
angles, with the exception of that of sixty degrees, may be varied
considerably.
Upon the side a, b, of the prismatic frame a, b, c, shown in the
accompanying diagram, is cemented a plate of thick crown glass, the
edge of which is represented by A, B, a, b. The end of this plate a, A,
is cut and polished at right angles or nearly so to the side of the plate.
Upon the end b, c, of the front of the prism a piece of thin plate glass is
cemented. The remaining side of the prism a, c, is closed. The prism
thus constructed having been filled with bisulphide of carbon is ready
for use.
The incident ray from the slit telescope of a spectroscope or from any
other source striking the polished end of the thick plate A, B, a, b, is
refracted to d, at which point passing into the bisulphide of carbon it
is refracted again, reaching the prism at e, when, as it passes into the air
it is again refracted, assuming the direction e, r, exactly coincident with
the incident ray I, R.
The
Dispersion of course accompanies these several refractions.
surface A, B, of the plate is not used, and therefore is ground rough or
covered so as to exclude unnecessary light.
The prism may be used obviously with either end towards the source
of light, but more than three times the despersion is produced when the
incident ray is received upon the broad end of the prism b, c, than when
used in the reverse position.
The advantages arising from this form of prism are as follows :-
First Its direct action is in all cases a most obvious advantage.

page_text: Second. When the incident ray from the slit telescope is received upon
the narrow end of the prism it gives fully the dispersion of an ordinary
sixty degrees bisulphide prism, and even with a wide slit gives great
uniformity and sharpness of definition.
Third. If the incident ray strikes the prism in the direction I', R, the
Fraunhofer lines are easily seen by the naked eye by means of the
prism alone, no slit or collimator being used, the light being taken from
a window or some large aperture. In this case the prism does not act
quite directly.
Fourth. By receiving the light from the slit telescope upon the broad
end of the prism the dispersion is so greatly increased that the polar
lines D¹ and D³ are so widely separated that the nickel line is readily
seen between them.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Joseph Beck in the Great Scal Patent Office
on the 25th August 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOSEPH
BECK, of Cornhill, in the City of London, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-fifth day of February, in the year of our
Lord One thousand eight hundred and seventy-five, in the thirty-eighth
year of Her reign, did for Herself, Her heirs and successors, give and
grant unto me, the said Joseph Beck, Her special license that I,
the said Joseph Beck, my executors, administrators, and assigns, or
such others as I, the said Joseph Beck, my executors, administrators,
and assigns, should at any time agree with, and no others, from time to
time and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within the
United Kingdom of Great Britain and Ireland, the Channel Islands,
and Isle of Man, an Invention for "AN IMPROVED PRISM FOR SPECTROSCOPIC
AND OTHER PURPOSES," a communication to me from abroad by Messieurs
James W. Queen and Company, of the City, County, and State of New
York, in the United States of America, upon the condition (amongst
others) that I, the said Joseph Beck, my executors or administrators, by
an instrument in writing under my, or their, or one of their hands

page_text: and seals, should particularly describe and ascertain the nature of the
said Invention, and in what manner the same was to be performed, and
cause the same to be filed in the Great Seal Patent Office within six
calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE, that I, the said Joseph Beck, do hereby declare
the nature of the said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by
the following statement thereof, reference being had to the Drawing
hereunto annexed and to the figures and letters marked thereon, that is
to say :-
This Invention consists in the construction of a prism cither hollow
and filled with bisulphide of carbon or other dispersive fluid or solid, of
glass or other transparent substance, in such a manner that the incident
ray and the mean ray of the emergent pencil shall be in the same right
line, that is, the action of the prism is direct, giving obvious advantages
over the common form.
The following is a description of the construction of the hollow
bisulphide of carbon prism, and will apply also to the construction of
solid glass prisms in cases in which the index of refraction does not vary
materially from that of bisulphide of carbon. It consists of a prismatic
framework of iron, brass, or other material having nearly the following
angles, namely, sixty degrees, thirty degrees, and ninety degrees. The
angles, with the exception of that of sixty degrees, may be varied
considerably.
Upon the side a, b, of the prismatic frame a, b, c, shewn in the
diagram, is cemented a plate of thick crown glass, the edge of which is
represented by A, B, a, b. The end of this plate a, A, is cut and
polished at right angles-or nearly so to the side of the plate. Upon the
end b, c, of the front of the prism a piece of thin plate glass is
cemented. The remaining side of the prism a, c, is closed. The prism
thus constructed having been filled with bisulphide of carbon is ready
for use.
The incident ray from the slit telescope of a spectroscope or from any
other source striking the polished end of the thick plate A, B, a, b, is
refracted to d, at which point, passing into the bisulphide of carbon, it
is refracted again, reaching the prism at e, when, as it passes into the

page_text: air, it is again refracted, assuming the direction e, r, exactly coincident
with the incident ray I, R.
The
Dispersion of course accompanies these several refractions.
surface A, B, of the plate is not used, and therefore is ground rough or
covered so as to exclude unnecessary light.
The prism may be used obviously with either end towards the source
of light, but more than three times the dispersion is produced when the
incident ray is received-upon the broad end of the prism b, c, than when
used in the reverse position.
The advantages arising from this form of prism are as follows:-
First. Its direct action is in all cases a most obvious advantage.
Second. When the incident ray from the slit telescope is received upon
the narrow end of the prism it gives fully the dispersion of an ordinary
sixty degrees bisulphide prism, and even with a wide slit gives great
uniformity and sharpness of definition.
Third. If the incident ray strikes the prism in the direction I', R, the
Fraunhofer lines are easily seen by the naked eye by means of the prism
alone, no slit or collimator being used, the light being taken from a
window or some large aperture. In this case the prism does not act
quite directly.
Fourth. By receiving the light from the slit telescope upon the broad
end of the prism the dispersion is so greatly increased that the polar
lines D¹ and D² are so widely separated that the nickel line is readily
seen between them.
Having thus described the nature of the said Invention and the mode
of carrying the same into effect, I would have it understood that what
I claim is, the construction of a direct prism, either hollow or solid,
substantially as described.
In witness whereof I, the said Joseph Beck, have hereunto set
my hand and seal, this Thirteenth day of August, in the year
of our Lord One thousand eight hundred and seventy-five.