Prismatic Compass Markings

#1
The old Prismatic Compass certainly in use in the 60's and 70's had the card which floated in the oil filled body marked , degrees version , North East South West . However around the outside of the body the cardinal points were marked N W S E ... why ? I believe they were withdrawn because the luminous markings were too radioactive .
 
#2
Because the prismatic compass works in reverse.

msr
 
L

Lizard_Lips

Guest
#8
Fallschirmjager said:
Lizard_Lips said:
Bravo_Bravo said:
And MFCs. No doubt FOOs, too.
We certainly do, however as for FOO's if they do theirs must be f*cked
I heard the Royal Irish had the best Mortar Pl in the British Army.
Mate you should see their MMG Pl re wrote the pamphlet by all accounts
 

TheIronDuke

ADC
Book Reviewer
#10
I thought they were withdrawn after July 8, 1947?
 
#12
Thanks for info . Have checked out website and read the explanation . It must be a survey thing to invert things ... I now remember the staff used for engineering survey work had to be read upside down through the " Dumpy Level .
 
#13
It's because you look at the markings through the prism - essentially a mirror.

The degrees version would have been withdrawn when the British Army converted to mils, though I would imagine that Air Controllers would have kept the degrees version, at least for a while longer.

The radioactivity issue may also be a fair point - I have a couple of old pocket watches and a Spitfire clock that caused my Physics teacher to sh!t himself when he was introducing us to the Geiger counter. And that was in the days when we were encouraged to roll mercury about in the palms of our hands :)
 
#14
putteesinmyhands said:
...The radioactivity issue may also be a fair point ...
Shit.

That explains my kid having 3 heads then.

Quite like the previous comment 'it must be a survey thing' - a bit like wandering aimlessly in the ulu at obscure hours whilst everyone else is eating/drinking/sleeping trying to find the lost BP, and screaming at people not to lean on the PADS wagon as 20 minutes of spinning up gets fecked out the window as some mong parks their arse on the bonnet


... and breath.
 
#15
putteesinmyhands said:
It's because you look at the markings through the prism - essentially a mirror.

The degrees version would have been withdrawn when the British Army converted to mils, though I would imagine that Air Controllers would have kept the degrees version, at least for a while longer.

The radioactivity issue may also be a fair point - I have a couple of old pocket watches and a Spitfire clock that caused my Physics teacher to sh!t himself when he was introducing us to the Geiger counter. And that was in the days when we were encouraged to roll mercury about in the palms of our hands :)
:D :D :D And steal metallic Sodium and stick in the school bogs. And taking the stopper off the Bromium container - for a laugh! Health and Safety my arrse 8)
 
#16
putteesinmyhands said:
It's because you look at the markings through the prism - essentially a mirror.

The degrees version would have been withdrawn when the British Army converted to mils, though I would imagine that Air Controllers would have kept the degrees version, at least for a while longer.

The radioactivity issue may also be a fair point - I have a couple of old pocket watches and a Spitfire clock that caused my Physics teacher to sh!t himself when he was introducing us to the Geiger counter. And that was in the days when we were encouraged to roll mercury about in the palms of our hands :)

My bold - I think the stuff was called 'Tritium paint' and was was used to 'highlight' the 'needle' particularly on altimeters.
 
#17
Anyone know the difference (if any) between the M73 and the M88 (other than colour)?

Cheers
JJ
Edited. M88 is largely made of alloy which makes it lighter and it's minimum operating temperature is 10 degrees C higher.
 
#18
JonnoJonno said:
Anyone know the difference (if any) between the M73 and the M88 (other than colour)?

Cheers
JJ
Edited. M88 is largely made of alloy which makes it lighter and it's minimum operating temperature is 10 degrees C higher.
They have two different numbers
:D
 
#19
IndianaDel said:
JonnoJonno said:
Anyone know the difference (if any) between the M73 and the M88 (other than colour)?

Cheers
JJ
Edited. M88 is largely made of alloy which makes it lighter and it's minimum operating temperature is 10 degrees C higher.
They have two different numbers
:D
That's the badger. Cheers (always wondered) :D
 
#20
The older prismatics had Radium as the radioactive source which is lousy stuff to deal with. The newer (green) ones use tritium which is more 'friendly'. There where two types available Mils and Degrees.

The new M88s are lighter and much cheaper but just as accurate.
 

Similar threads

Latest Threads