SLIDING SCALES FOR ENGINEERING CALCULATIONS
Year: 1884

page_text: "
IDIONAL
DIECIFICATION.
I LALA GANGA RAM C.E. Executive Engineer Public Works Department Punjab
in the Empire of India at present residing at 30 Guildford Street Russell Square in
the County of Middlesex do hereby declare the nature of my Invention for
SLIDING SCALES FOR ENGINEERING CALCULATIONS " to be as follows:-
"
:-
This Invention has for its object sliding scales for engineering calculations.
My scales for scantlings of timber in flat roofs and for strains on pitched roofs
is applicable to any timber with any ratio of breadth to depth and to any form of
truss (with horizontal tie) up to 70' span.
The rule is shown by Figures on the. Drawing annexed. Figure 1 is the obverse,
Figure 2 is the reverse. Figure 3 is the edge.
In Figure 1 the scales A. A relate to the span, and the scales D D to the ratio of
breadth to depth. These scales are on two parallel pieces of boxwood held
together by metal straps X X and the slider marked B works between them. The
slider has upon it four scales, two relating to the depth of the beam or piece and
the others to the efficiency of the material as regards strength and stiffness
respectively.
The upper and the lower rules each carry also an ivory slider marked C with a
scale upon it relating to the load upon the roof.
The side of the slide rule indicated by Figure 1 is adapted to flat roofs, the other
for trusses.
DIRECTIONS FOR USE.
Flat roofs. First set the arrow mark on C against the required ratio of breadth
to depth on D. Then place the co-efficient (of timber) marked on slide B against
load (per foot run = weight per superficial foot x spacing centre to centre) marked
on vernier C, and against span in feet on A look for depth (in inches) on B.
For trusses. From the slide rule, the strains on principal rafter and tie-beam
may be found. In the former case the result is the maximum strain which is always
on the lowest member.
The scales shown by Figure 2 are employed. The upper rule has upon it two
scales, one relating to the span of the principal rafter and the other to the slope of
the roof. The lower rule has also a scale relating to the slope of the roof and

page_text: another relating to the span of the tie beam. The slider has upon its edges two
similar scales relating to the strain and between them two scales relating to the
. load upon the roof.
DIRECTIONS FOR USE.
Place the load mark on B against the slope on A and against span on A read
strain in pounds on B.
A slide rule for indicating the thickness to be given to retaining walls, is
constructed as follows:-
The slide rule is represented by the Figures 4 and 5 one the obverse the other the
reverse. It consists of a main rule usually of boxwood and two sliders one I make
in wood and the other in ivory. The main rule has upon it three scales, (1) the
natural slope of the pressing material (2) the height of the wall in feet (3) a scale
applicable to surcharged walls and marking the slope above the top of the wall.
The wooden slider has upon it in duplicate a scale for wall thickness and a scale
for the weight of the wall per cubic foot. The ivory slider is marked with a scale
for the weight of the pressing material in pounds per cubic foot. The scales may
of course be in other units.
The reverse side of the slide rule has upon it as will be seen directions for use and
also tables and for adapting the theoretical result obtained to the varying
circumstances of practice.
A slide rule for indicating strains on girders is constructed as indicated by the
Figures 6 and 7. Figure 6 is the obverse and Figure 7 is the reverse.
The scales on one side are adapted to finding bending, strains and those on the
other side for finding shearing strains on any girder, (plate or flanged) of any
shape and of all practical spans.
The scales for bending strains are then arranged in two sets, the upper give
bending strains at centre and the lower give the same at any other point.
The scales for shearing strains are also arranged in two sets the upper indicating
such strains on any bar inclined at any angle as are due to uniform load and the
lower indicating the strains due to a passing or travelling load.
Dated this 25th day of January 1884.

page_text: The main rule has upon it three scales (1) the natural slope of the pressing
material (2) the height of the wall in feet (3) a scale applicable to surcharged walls
and marking the slope above the top of the wall. The wooden slider has upon it
in duplicate a scale for wall thickness and a scale for the weight of the wall per
cubic foot. The ivory slider is marked with a scale for the weight of the pressing
material in pounds per cubic foot. The scales may of course be in other units.
The reverse side of the slide rule has upon it, as will be seen, directions for
use and also tables for adapting the theoretical result obtained to the varying
circumstances of practice.
A slide rule for indicating strains on girders is constructed as indicated by the
Figures 6 and 7. Figure 6 is the obverse and Figure 7 is the reverse.
The scales on one side are adapted to finding bending strains and those on the
other side for finding shearing strains on any girder (plate or flanged) of any shape
and of all practical spans.
The scales for bending strains are then arranged in two sets, the upper giving
bending strains at centre and the lower giving the same at any other point.
. The scales for shearing strains are also arranged in two sets, the upper indicating
such strains on any bar inclined at any angle as are due to uniform load, and the
lower indicating the strains due to a passing or travelling load.
It is obvious that these scales can be made of any material such as metal, ivory,
card-board, wood, or a combination of any such materials.
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 adaptation of the logarithmic scales with different radii, combined with
such modifications and arrangements as to serve the solution of engineering
formulæ mechanically, substantially as described in the Specification and illustrated
in the Drawings Figs. 1 to 7.
2. The several and respective combination of parts together forming my improved
sliding scales for engineering calculation herein before described and shewn on the
Drawings or any mere modification thereof.
Dated this 28th day of July 1884
GEO. DOWNING,
Agent for Applicant.