View Full Version : Hillman Mirror/Hill's Mirror

Peter Kirk
08-08-2010, 20:53
Another mystery (to me at any rate). A number of pre-war and early wartime bombing range plans show a Hillman Mirror or sometime a Hill's Mirror near the master quadrant. So far I have found no pictures of one and have no idea as to its purpose or what one looks like.

There is a drawing number for the base of one and one of Richard Drew's photos caught my eye whilst anguishing over Brean.


Could the circular disc be for one of these mirrors? Sadly I have found no plan for Brean so I cannot confirm this.

Paul Francis
08-08-2010, 20:59
The archives has a picture of one at Orfordness, or at least the framework that supported the mirror. Might take a while to locate though.

Paul Francis
08-08-2010, 21:15
Seems the system works very well. Hills Mirror, Orfordness 1994

Peter Kirk
08-08-2010, 22:47
Fantastic. I was beginning to think they were mythical. All I need now is what they were used for and how also when they stopped being used. And.......

09-08-2010, 08:41
When NP mentioned the one at Orford Ness I though he was referring to the revolving drum device with peripheral mirrors and a central light source used to project a flickering beam vertically where it illuminated a falling bomb which was filmed during the drop. This (somehow) made judgement of the bomb ballistic possible. But, as far as I know that was a post-war system.

The image NP has posted looks like a frame that held a circular mirror that could be angled. I opine that, it was used to reflect the light of the flashbulb fired by the aircraft to indicate 'bomb gone'. Since the aircraft would be almost overhead at the point of release, and the range crew were inside the quadrant shelter (QS) with a roof over their heads the mirror could be angled so that an observer in the QS could see 'bomb gone'. I'm talking now about ranges which did not communicate using RT but with visual signals only.

I anticipate that the actual mirror would have been hemispherical to give a large field of view and located near to the Master Quadrant.

Anyone know otherwise?

Paul Francis
09-08-2010, 09:16
Its a pre-war device, as described by Peter's second paragraph. at least that is my understanding.

Peter Kirk
16-10-2010, 13:53
RAFM has details of the Hills Mirror (AP 1243 dated 1937 - I think) and shows it to be a flat table with a mirror laid horizontally and adjusted to face magnetic north and perfectly level. It was used to measure speed/direction of wind via smoke puffs from aircraft or aircraft speed and direction. Measurement was via a simple sight angled at 45 deg and used to view movement which was plotted via a grease pencil on the mirror. Speed was measured using a stop watch or metronome to mark locations at timed intervals.
It was suggested that the best location would be a compass platform so in the context of a Bombing Range it would explain the specific design for a Hills Mirror base.

The photo NP posted above has nothing in common with the pre war design which required a strictly level surface. The question is what was the photo of then as it certainly looks like it could be a reflector of some sort?

16-10-2010, 17:12
NP - is your photo from 'The Field of Mirrors', about which I've heard you mention, but know absolutely nothing about?


17-10-2010, 06:00
See my Post # 5 - NPs picture is nothing like the Mirrors, Observation (Hill's Mirror) details of which PNK has uncovered so maybe it is something to do with the bomb ballistic unit?

Peter Kirk
18-10-2013, 18:42
Just been flicking through "Most Secret- The Hidden History of Orford Ness" by Paddy Heazell and came across the field of mirrors reference (Page 184). It was by the bomb ballistics building but the author states "Its proper name was an array of Hill' mirrors". I'm not sure that is correct or at least not the Hill's mirrors used by the RAF. As I have already said these required to be perfectly level and would not have suited the environment it they would have been subjected to. To have a field of these would have required a solid concrete base for each one. However it is entirely possible that Hill's could have referred to another type, specific to the Orford Research Station in which case the photo NP posted is possibly one of the field of mirrors. The author did imply the there was certain amount of exaggeration in the term "field of mirrors" so it may have been something simpler than the description implies.

Peter Kirk
18-10-2013, 19:33
The link below shows the Hills mirror as used by the Army and RAF, although the RAF version may differ slightly. Since it required at least one operator to mark the track of the target you can see why I am sceptical about the ORS use of this particular type.


Paul Francis
18-10-2013, 22:51
I wonder if the Orfordness example is some kind of Schlieren mirror?

19-10-2013, 03:42
I should think that the manufacturer of 'Hill's' mirrors, being a specialist, would have manufactured different types of mirror assemblies for the military and Government and each would have been a 'Hill's'.

Now that PNK has researched the Hill's mirror assembly used for aircraft tracking it is clear that the Orford Ness mirror is different and may, in my opinion, be one of a circular array used by the Bomb Ballistic Unit.

Peter Kirk
19-10-2013, 11:15
I wonder if the Orfordness example is some kind of Schlieren mirror?

Could be as the miniature firing range did use high speed "spark" photography. If this was the case there must have been a few!