1098

THE COLLIERY GUARDIAN.

May 31, 1918.

possible temperature to be attained was the same as
before, viz., 1,300 degs. Cent.

These tests show clearly the great advantage of gas
firing in a scientific way. The old combustion
chambers at small boiler loads were able to give about
the same results as regards composition of the chimney
gases. By using gas burners no combustion chambers,
with their high radiation losses, were required and
a better transfer of heat could be made, resulting in
a higher boiler load and better efficiency.

Whilst in the case of large boilers one may adjust
the variations of pressure, air supply and chimney
draught automatically, this is not likely to be done
at most plants, and one will have to rely on the
control of the boilers by more or less skilled men.
These men must have the apparatus necessary for
boiler control, and much more attention must be paid
to the supervision of the results than has been done.
Boilers fitted with the best combustion arrangements
will give results 5 per cent, better if intelligently
controlled than they will give if run by the usual
boiler men uncontrolled. In every works raising large
amounts of steam there should be a man whose business
is simply to see that the maximum possible efficiency
is always maintained. The salary of such a man would
be many times repaid by the additional steam for
which he would be responsible. If the boiler men
could earn a small premium for maintaining good
results, they would quickly see that it was to their
interest to study the results they were getting. They
would reduce economy in boiler firing to a fine art, to
the great advantage of the owners of the plant.

MIDLAND COUNTIES INSTITUTION
OF ENGINEERS.

A general meeting of the members of the Midland
Counties Institution of Engineers was held at the
University College, Nottingham, on Saturday, May 25,
under the presidency of Mr. Geo. Spencer (West
Hallam).

NEW MEMBERS.

Mr. G. A. Lewis, the secretary, announced the elec-
tion of the following. Subscribing firm: Messrs.
Hall’s Collieries Limited, Swadlincote, Derbyshire.
Members: J. W. Calder, colliery surveyor, Mapperley,
Collieries, near Derby; H. Shelton, colliery manager,
West Hallam, Derby. Associate: T. Bonser, under-
manager, ‘‘Brooklyn,” Nottingham-road, Eastwood,
Notts.

NOMINATION OF OFFICERS.

The Secretary further announced the following list
of nominations of officers for the year 1918-19, which
had been prepared by the council under Rule 24:
President, Mr. H. Eustace Mitton (Butterley Col-
lieries. Vice-presidents: Mr. T. P. Barber, Mr. H.
Dennis Bayley, Mr. E. E. Bramall, and Mr. J. Mein
(vice-presidents of the current year), and Mr.
C. Dickinson, Mr. C. M. Haslam, Mr. C. R. Hewitt,
and Mr. F. N. Iliffe (new nominations). Councillors:
Mr. J. Bingley, Mr. F. Chambers, Mr. R. H. F.
Hepplewhite, Lieut.-Col. R. Pemberton Leach, Mr.
H. March, Mr. W. Tate, Mr. David N. Turner, and
the following new nominations: Mr. H. O. Bishop, Mr.
B. McLaren, Mr. C. W. Phillips, Mr. S. Evans, and
Mr. W. H. Goodwin.

MAGNETIC DECLINATION.

The President contributed some notes on “ Mag-
netic Declination,” with special reference to the tables
published weekly by the Meteorological Office. He
remarked that the magnetic compass had been em-
ployed from the early days of mining to enable the
miner to locate his workings in relation to the sur-
face. In its form adapted for mining work, known
as the miners’ dial, it was to-day almost universally
used, except in cases where great accuracy was re-
quired, and would probably never be entirely super-
seded. As an instrument of precision it could not
compare with the transit theodolite for important
surveys such as main roads, drivings or workings to-
wards a boundary, but for general work underground,
where great accuracy was not required, the miners’
dial was a most useful instrument. Its utility, how-
ever, might be vastly increased by the employment
of the tables of magnetic declination now published
weekly in the Colliery Guardian and the Iron and
Coal Trades Review, and monthly in the Transactions
of the Institution of Mining Engineers. The chief
objection to the use of the magnetic compass in
making mining surveys had been that the needle did
not point in a constant direction; in other words, that
the declination was not constant. Reference to the
magnetic tables showed that the mean declination
value for April 1917 was (for Kew) 15 degs. 1*3' W.,
and for April 1918 it was 14.52, or diminution of 93'
This was the annual variation, and 10' might be stated
to be the amount for this country during the present
year within the range accuracy of mine surveying.
Allowance was usually made by the min© surveyor for
this variation according to the time which had elapsed
since the previous magnetic meridian was put upon
the plan. But in addition to the annual variation
there was another and far more considerable varia-
tion which was seldom recognised or allowed for,
namely, the diurnal variation. Whereas great pains
were usually taken to make the correction for the
change due to, annual variation, the diurnal variation
was almost entirely ignored. The daily range, or the
difference between one extreme and the other, might
amount to 20' or 30', or even more. During April 26,
for instance, of the present year the difference of decli-
nation between midnight and noon amounted to 24' of
arc, as might be seen from an inspection of the tables
published for the week ending April 27. Such
differences were not frequent, but they did occur,
and it might be remarked that, the present year
being one of great disturbance on the sun’s surface,
great magnetic disturbances might be expected.
These diurnal variations, apart from magnetic storms,
were by no means regular throughout the year. They
were least during the winter months and most during

the summer months. The declination was nearest the
mean daily average from 5 o’clock in the afternoon
—or 17 o’clock—to 4 o’clock in the morning. From
this fact it was obvious that the best time for making
underground surveys of any importance would be
during these hours. It was equally obvious that
accurate plans could not be made from magnetic
surveys unless proper corrections were made for the
variations of the direction of the compass from a
given meridian. To illustrate a case, let it be assumed
that a survey of part of a mine was to be made in
order to ascertain the position of a certain point in
relation to the surface—it might be to check the
workings approaching or skirting a boundary, say,
2,000 yards from the pit bottom. The bearing of the
test line on the surface would be taken, from which
the magnetic meridian was to be drawn. He would
assume that this was taken at 9 o’clock a.m. At
this hour, it might be noted, the declination was near
its minimum. The survey itself was commenced at
1 or 2 o’clock in the afternoon. At this hour the
declination would be at, or near, its maximum.
Following the usual procedure, the dial was set in
a working place cleared of rails or other material
which attracted the needle, and the survey was carried
on to the pit bottom. A check might possibly be
obtained when nearing the end of the survey, and
the chances were that the north end of the needle
would not coincide with zero of the dial. Normally
the difference should be 6', the declination in the
meantime having diminshed by this amount. The
meridian from which the work was to be plotted
having been taken when the declination was at its
minimum, and the work having been done from
a meridian at the time of maximum declina-
tion would account for an error of 10' or 12'
—by no means a neglible quantity in a distance
of 2,000 yards, the deviation being, in fact, about
six yards. It might be remarked that he had
taken an extreme case. This was possibly true, but
such cases could happen. Again, normal departures
had been taken, but there were times when the range
of declination might vary from two to three-fold the
amounts given, in which cases the error would be corre-
spondingly greater. The declination tables furnish
the mining surveyor with data which, if properly
applied, would enable him to correct his work for
such errors, due to change of declination, and should
result in more accurate plans being kept. If in the
previously assumed survey the correction due to the
hour when taking the meridian had been applied,
the error would have been reduced nearly one-half,
and, further, if the proper correction had been applied
to the bearings of the lines of the survey—or prefer-
ably to the meridian from which the survey was
plotted—practically all errors due to variations of
declination might have been eliminated. It would be
observed that the published tables were of great value
to the mining surveyor, furnishing him, as they did,
with data never before available for correcting his
work and enabling him to keep his plans more
accurately. Where still greater accuracy was re-
quired he suggested that the work be provisionally
corrected as previously described, and on receipt of
the published weekly data any further correction
which might be found necessary could be applied. In
concluding, the President said that his object was to
stimulate discussion. Although their surveys in the
past might have been inaccurate, the marvel was that
they had achieved such a degree of accuracy consider-
ing the variations in the declination.

DISCUSSION.

Mr. H. E. Mitton (Butterley), after remarking
that the paper had introduced quite a new subject
to them, and that surveyors were well represented
there that afternoon, said that he should like very
much to know whether it was at all customary to
consider this diurnal variation. As far as he was
concerned it had never come into consideration, and
he should be very much surprised to learn that any
of them had taken it into account when making sur-
veys. He thought the paper was so important that
the discussion upon it should be adjourned, and that
at the next meeting they should go into the matter
a little further and deal with what he might call
the shrinkage of plans. When on the Continent he
had been immensely struck with the fact that the
plans were kept in squares, and he thought that the
Institute-might usefully consider whether rolled plans
were best for a colliery.

Mr. R. F. Percy (Nottingham) said that Mr.
Mitton’s question was a very pertinent one, but the
answer was that they had not taken into considera-
tion the diurnal motion of the needle. It was not
because they did not know about it, but in the first
place they had no definite information which would
serve them when they wanted to adjust matters, and
in the second place there had been an impression
that the difference was so small as to be negligible.
In addition to the diurnal variation there was also
a seasonal variation—the difference, say, between
spring and autumn, which might be greater than that
between 3 o’clock in the afternoon and 11 o’clock
at night. In the olden days surveyors took the
meridian in the morning and made the survey in the
afternoon, which was about the worst thing they
could do. A much better plan was to make the survey
one morning and take the meridian the next morn-
ing, or, better still to take the meridian on Monday,
make the survey on Tuesday, and then take the
meridian again on Wednesday and adopt the mean.
He was struck with a report in the Colliery Guardian
of that day, showing that on the 14th inst.—just over
a week ago—at 3 o’clock in the afternoon the mag-
netic meridian was 14 degs 58 mins., and at
11 o’clock the same night it was 14 degs. 36 mins.—
a difference of no less than 22 mins, in the same day. If
a surveyor had taken his meridian at one time and
made his survey at the other, there would be an in-
accuracy represented by 22 mins.—a difference of over
one-third of a degree, or 1 in 160, which was a very
serious thing. Even a 11 common or garden” sur-
veyor ought to get nearer than one-third of a degree.

Having provided the tables, the next thing was how
to insist that they should be observed. Unfortunately,
mine surveying was an ill-paid profession, and they
frequently got a second-class man to do a first-class
job. Unless something were done to raise the status
of the profession they would have men using the dial
who cared nothing for the accuracy of the task on
which they were engaged. He suggested that it would
be a good plan to instruct the surveyor to write down
in each case what the declination was at the time
he made his survey. The colliery manager should
then from time to time look out the survey book and
see that the tables had been duly observed. If that
were done a surveyor would be a little more particular
about using the tables. One very important question
was, What degree of accuracy was really wanted?
They might think this over and, when the discussion
was resumed at the next meeting, bring the answer
with them. Some years ago a great authority on mine
surveying told him that he would be satisfied with
ten yards in a mile. With reference to plans, there
was no doubt that the German system was a very
good one. They used small plans, like the small sheets
of our 6 in. Ordnance map, though as they worked
in metres the scale was less than ours. They were
made on the stiffest and hardest cardboard, and fitted
closely and accurately together. Each plan was kept
in a separate drawer, and there were perhaps 20 or
30 drawers in a cabinet in the office. It was impos-
sible to bend them, and they would neither break
nor crack; they were not only accurate, but models
of what plans ought to be. The members of the
institute were particularly indebted to the president
for his valuable address. He (the speaker) had often
wished that some one in an official position would
bing the subject before them, so that members would
realise more clearly the extraordinary changes which
took place in the magnetic meridian.

Mr. J. Mein (South Normanton) supported the
suggestion that the discussion should be adjourned,
and moved a vote of thanks to the president for his
paper, which was cordially agreed to.

The President said that he should be pleased for the
discussion to be adjourned, as it was impossible to
thresh out such a subject in one afternoon. With
regard to the use of squared paper for plans he might
say that he had practised that for a number of years.
They divided the paper into ten-chain squares, and
the lines had reference to the true north and not
the magnetic north. Mr. Percy had opened up a
fresh side of the subject by touching on the seasonal
variation, for there was no doubt that that was greater
in some cases than the diurnal; but all these would
be seen in the tables. It was only two months since
the tables were commenced, and they were now
approaching the time of the greatest variation—May,
June and July. In the winter it was normally almost
negligible, but they got occasionally magnetic storms
which disturbed the needle and sometimes deflected
it to half a degree. He remembered once making
a survey when the needle would not settle at all.
He could not understand it at the time, but after-
wards he discovered that there had been a magnetic
storm, which had caused the extraordinary deflection
of the needle. With regard to the degree of accuracy
required, he agreed that that was a point which needed
settling, and he thought that the time had come
when the whole matter of surveying ought to be con-
sidered by the Institution of Mining Engineers. A
committee might be appointed to take the evidence
of practical surveyors and to ascertain what was pos-
sible—or perhaps he ought to say practicable. A great
deal depended upon the object in view. What was
physically possible might not be commercially possible.
If they wanted merely to fix the place for a gate or
anything of that sort, extreme precision was not re-
quired, but if a question of boundary was involved
the strictest accuracy was demanded. A bad survey
might lead to an action for trespass, or perhaps to
•an encroachment upon old workings, accompanied by
inundation and disaster. Some owners, rather than
run any risk, would probably leave a good big barrier,
but surveyors ought to be able to work with such
accuracy as to render quite unnecessary an expedient
of that kind.

The discussion on the subject was then adjourned
until the next meeting

PIT TIMBER.

Mr. J. Bingley (Bolsover) introduced a discussion
on “ Pit Timber,” with special reference to an
appliance now in use at Bolsover Colliery. In the
course of his remarks he said that, the usual sources
of supplies being restricted, and supplies of home-
grown timber being limited and of inferior quality,
there was great necessity for economising. This
could be done not only by utilising short pieces which
would otherwise be wasted at the source, but also
by salvaging broken props extracted from workings.
The life of an ordinary timber pit prop was limited,
for in many cases where excessive roof movement
existed it was only capable of being used once; under
favourable conditions it might be used twice or three
times, especially after the first time for “lining up”
purposes. Most props broke into irregular lengths.
A 5 ft. or a 6 ft. prop breaking into two pieces was
capable of being sawn into lids or, in exceptional
cases, into sleepers, but much waste ensued. The idea
of the Bolsover pit prop socket was to utilise these
broken parts indefinitely until it was impossible to
use them any further. The socket would join pieces
of irregular length together, according to the length
of prop required. If, for example, a 6 ft. prop were
required, pieces of 3 ft. in length, 4 ft. and 2 ft. or
5 ft. and 1 ft. might be used. These pieces were
tapered at the ends introduced into the socket, and
might also be tapered at either or both ends coming
in contact with the floor and roof. The socket was
constructed of a double thickness of steel tubing. The
inner part was tapered from the extremities, so that
the tapers met at the centre of the tube; or there
might be a short cylindrical portion of some three or
four inches in the centre, the taper springing from
each end of this part to the extremity of the tube. An