[JR79]

Hi,

I've been involved in local history for many years but have never heard of the 1929 6 inch OS map as refered to on the national monuments viewer on archaeology.ie.

I have used the 1829-41 & 1897-1913 OS maps many times but have never heard of the 1929 edition.

Does anyone have an info on this map.Had a look at osi.ie & the internet in general but came up with nothing.

[Riamfada]

Never heard of it myself.

[slowburner]

Originally Posted by JR79

Hi,

I've been involved in local history for many years but have never heard of the 1929 6 inch OS map as refered to on the national monuments viewer on archaeology.ie.

I have used the 1829-41 & 1897-1913 OS maps many times but have never heard of the 1929 edition.

Does anyone have an info on this map.Had a look at osi.ie & the internet in general but came up with nothing.

Maybe it's a typo - easy enough to misplace one digit like that. I couldn't find any reference to a 1929 map either here or here

[Aelfric]

I've come across many editions of the OS over the years - there were many revisions after the 1st edition (1840s), 2nd edition (early 1900s), right up until the 1950s.

[slowburner]

Originally Posted by Aelfric

I've come across many editions of the OS over the years - there were many revisions after the 1st edition (1840s), 2nd edition (early 1900s), right up until the 1950s.

First national survey 1837 - 1842.
Second national survey 1888 - 1913.
There was a 1" map produced in 1851.
Between 1857 - 79 the 1:500 urban survey was produced.
See here


On a slightly different note. Does anyone know if there is a significant difference between magnetic north in 1842 and today?

[Red Harvest]

Originally Posted by slowburner

First national survey 1837 - 1842.
Second national survey 1888 - 1913.
There was a 1" map produced in 1851.
Between 1857 - 79 the 1:500 urban survey was produced.
See here


On a slightly different note. Does anyone know if there is a significant difference between magnetic north in 1842 and today?

Isn't the yearly decrease printed on the map?

The actual figures for Mag, True and Grid North are normally printed with reference to a specific date then the annual change is alongside.

afaik (and I could be miles off) there should be a refence North South Grid line which has the deviations written at the top of it or there might be a side box/bottom box with the info referencing where on the map the figures are true for.

...... just been and grabbed the nearest OS map I could find, Discovery Series here and all the info is in a box on the rt hand side of the map. Says 08.6' annual decrease (as of 1995 for sheet 82) now that might not hold out very well over 150years

But I'm sure that info is at the top somewhere on the old 1:63,000 1inch maps?

[slowburner]

Originally Posted by Red Harvest

Isn't the yearly decrease printed on the map?

The actual figures for Mag, True and Grid North are normally printed with reference to a specific date then the annual change is alongside.

afaik (and I could be miles off) there should be a refence North South Grid line which has the deviations written at the top of it or there might be a side box/bottom box with the info referencing where on the map the figures are true for.

...... just been and grabbed the nearest OS map I could find, Discovery Series here and all the info is in a box on the rt hand side of the map. Says 08.6' annual decrease (as of 1995 for sheet 82) now that might not hold out very well over 150years
Thanks Red Harvest.
But I'm sure that info is at the top somewhere on the old 1:63,000 1inch maps?

If there was a continuous decrease of 0.086' over 150 years then the overall shift would be 12.9º - does that seem any way realistic?
(08.6' gave a shift of 1,290º when I plugged it into the calculator).

I couldn't see anything on the OSI mapviewer to help calculate the deviation.

The actual amount doesn't really matter to me - knowing that there is a significant shift is good enough.

[Red Harvest]

Originally Posted by slowburner

If there was a continuous decrease of 0.086' over 150 years then the overall shift would be 12.9º - does that seem any way realistic?
(08.6' gave a shift of 1,290º when I plugged it into the calculator).

I couldn't see anything on the OSI mapviewer to help calculate the deviation.

The actual amount doesn't really matter to me - knowing that there is a significant shift is good enough.

omg, when was the last time I did this stuff 30+ years ago

Check here then recalculate, because thats degrees and MINUTES we are dealing with so the calculation is 8.6 Minutes TIMES 150 Years then DIVIDED by 60 to get the answer from Minutes back to degrees. About 20degrees which still sounds alot to me.

I'll see if I have some really old maps with the variation on them I know I've some early 1:500 maps as jpegs on the computer somewhere.

Found the 1923 revision 1:500 maps I have but no magnetic variation info on them. Amazingly a 1:252440 (1/4inch) Bartholomews touring map I had to hand from 1969 had Mag variation as 10 Degrees 20 Minutes West with an annaul decrease of 8.5 minutes. Good maps btw for locating all the old "big" houses and estates.

[slowburner]

Originally Posted by Red Harvest

omg, when was the last time I did this stuff 30+ years ago

So, so long ago that you forgot it is called the declination angle

Check here then recalculate, because thats degrees and MINUTES we are dealing with so the calculation is 8.6 Minutes TIMES 150 Years then DIVIDED by 60 to get the answer from Minutes back to degrees. About 20degrees which still sounds alot to me.

I'll see if I have some really old maps with the variation on them I know I've some early 1:500 maps as jpegs on the computer somewhere.

Found the 1923 revision 1:500 maps I have but no magnetic variation info on them. Amazingly a 1:252440 (1/4inch) Bartholomews touring map I had to hand from 1969 had Mag variation as 10 Degrees 20 Minutes West with an annaul decrease of 8.5 minutes. Good maps btw for locating all the old "big" houses and estates.

I am thick.

20º sounds like a heck of a lot. Put in context (according to my numerically dyslexic calculations), if I wanted to head due north and I used a map from the early 19th C and a compass calibrated for today's magnetic north, then I would end up heading north east (?).

Here's an interesting snippet.

True north is a bearing in the night sky that lies within 0.5 degrees of Polaris, the North Star. Geographic north (the north geographic pole) is located at the point where Earth’s rotational axis pierces the Arctic ice. Magnetic north (the north magnetic pole) is the spot where Earth’s invisible magnetic field lines burst from the surface and point directly upward. While the north geographic pole is fairly stable, the north magnetic pole moves. Now located in the Arctic Ocean just north of Canada, the north magnetic pole is moving northwest toward Siberia by about 50 km a year. At its current rate, the north magnetic pole will pass within 400 km of the north geographic pole in 2018. The first explorers to find the north magnetic pole did so at Cape Adelaide, on the west coast of Canada’s Boothia Peninsula, in 1831. In the following century, the pole moved more than 1,300 km toward the northwest, along the same path it is taking today. (Sid Perkins, “North by Northwest,” Science News, 12/22&29/07)

[boneless]

I could be way off here, but was the first Sites and Monuments Record survey carried out in 1929? It was based on the 6 inch OS map, but as an amended survey it got it's own year maybe?

[Gee Bag]

Sites & Monuments Record (SMR) was only set up after National Monuments Act 1994. It was later superceeded by the Reord of Monuments & Places (RMP). The archaeological survey of Ireland was set up in the 1930's but didn't actually do anything until the Megalithic Survey of Ireland started in the 1940's. The current Archaeological Survey of Ireland began work in the late 70's or early 80's. The results of this survey are the basis for the SMR and RMP.

If the map is dated 1929 it is probably one of the various Ordnance Survey revisions. The dates for re-surveys vary from county to county.

[boneless]

Originally Posted by boneless

I could be way off here, but was the first Sites and Monuments Record survey carried out in 1929? It was based on the 6 inch OS map, but as an amended survey it got it's own year maybe?

I left out the wee word "if" at the start of the last bit