IMPROVEMENTS IN PROTRACTORS AND IN MARKING PROTRACTORS UPON MINING AND OTHER PLANS AND PAPERS, AND IN CORRECTING PROTRACTORS MADE ON PLANS AND PAPERS FROM TIME TO TIME, ACCORDING TO THE VARIATION OF THE MAGNETIC MERIDIAN
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by Henry Johnson, the younger, at the
Office of the Commissioners of Patents on the 22nd April 1880.
HENRY JOHNSON, the younger; of West Bromwich, in the County of Stafford,
Mining Engineer and Mine Manager. "IMPROVEMENTS IN PROTRACTORS AND IN
MARKING PROTRACTORS UPON MINING AND OTHER PLANS AND PAPERS, AND IN
CORRECTING PROTRACTORS MADE ON PLANS AND PAPERS FROM TIME TO TIME,
ACCORDING TO THE VARIATION OF THE MAGNETIC MERIDIAN."
In protractors marked on mining and other plans and papers errors are liable to
occur in consequence of the changes in the magnetic meridian which are constantly
going on.
The object of my Invention is to prevent or to correct theso errors. This I
effect by the improvements, herein after described, in the protractor by which the
marked protractor is produced on the plan or paper, together with the method,
herein after described, of correcting the marked protractor from time to time by
changing the direction of the zero line.
I will herein after distinguish between the instrument called the protractor and
the fac-simile produced on plans and papers, also generally called in mining the
protractor, by calling the latter the marked protractor.
I make the frame of the protractor double (whether the protractor be circular or
rectangular), one of the parts being less than and situated within the other, a space
of uniform breadth being left between them. The two parts of the frame are
connected together by bridge like connecting pieces. The space between the two
parts of the frame is occupied by a thin metal plate having a series of perforations
on the same radii as the divisions of the protractor.
In using this protractor it is placed in the proper position on the plan or paper,
and by means of the pigment carmine rubbed up with water and applied by a
stencilling brush I produce on the plan or paper in carmine the series of divisions
in the perforated plate of the protractor. When by the change in the magnetic
meridian the position of the marked protractor on the plan or paper requires
correction I bleach or discharge the carmine marked protractor by means of a
solution of chloride of lime or bleaching powder. After the bleaching has been
effected the bleaching solution is removed by blotting paper and washing with
water, and the plan or paper is thoroughly dried. The protractor is applied to the
plan or paper with a change in the direction of its zero line corresponding to the
change which has taken place in the magnetic meridian, and a marked protractor
....מ

page_text: produced by stencilling. This correction is made from time to time with a
frequency depending on the degree of accuracy which the nature of the particular
plan or paper renders desirable.
Instead of making the protractor by which the stencilling is effected, as herein
before described, it may be made in one pieco of the ordinary form, a broad groove
being made all round within the graduated edge; the said groove being of such a
depth that the metal at the bottom of the groove is sufficiently thin for the
stencilling perforations herein before described to bo conveniently made in it.
Although I prefer to use carmine and bleaching powder for the production and
removal of the marked protractor upon the plan or paper, yet I do not limit mysolf
thereto, as other pigments may be used and their removal effected by mechanical
means.