Ski Posted 15 July , 2004 Share Posted 15 July , 2004 Hello all, I've had this item for a while and was wondering if any Forum members had any idea of it's origin. I believe that Artillery used Angle of sight Intruments to lay guns, however i don't know if this just such an item or not. It looks military to me and you can see there is an arrow at the top of the instrument although it is not the usual broad arrow used by the War department. The eye piece on the left and the piece on the right fold out enabling you to line up the two which then gives you a reading of angle. Also underneath the white dial is a prismatic compass. The inscription on the front reads: ANGLE OF SITE INSTRUMENT H.A. MARK 1 J.H. STEWARD LTD 1916 NO. 217 Any ideas?? Cheers Ski Link to comment Share on other sites More sharing options...
Ski Posted 15 July , 2004 Author Share Posted 15 July , 2004 And the case...... Link to comment Share on other sites More sharing options...
CSMMo Posted 15 July , 2004 Share Posted 15 July , 2004 This may be totally off base, but as a modern day Artilleryman, this angle is needed to compute fires that clear intervening crests. If the computed angle of elevation goes below that angle (Called Range to Crest in the US Army), the mission has to be recomputed, i.e., a high angle of fire has to be computed or the mission handed off to another fire support weapon. That MAY be what this was used for, as we usually just sited down the tubes and I've never seen an instrument like that! Mike Morrison Link to comment Share on other sites More sharing options...
PhilB Posted 15 July , 2004 Share Posted 15 July , 2004 This seems to be associated? Phil B http://www.vickersmachinegun.org.uk/1951/glossary.html Link to comment Share on other sites More sharing options...
johnreed Posted 15 July , 2004 Share Posted 15 July , 2004 The angle of sight is the angle between two heights. This being the heght of the Gun position and the height of the target in the horizontal plane, for example the height of the gun position is 40 feet and the height of the target is 193 feet a difference of 153 feet and the range to the target is 3,000 yards. 1 degree subtends 51 feet at 1,000 yards, at 3,000 yards 1 degree subtends 153 feet at 3,000 yards. Therefore you have to add 1 degree to the quadrant elevation to adjust the range as if the gun and target were on the same height. I hope my explanationmakes sense. John Link to comment Share on other sites More sharing options...
PhilB Posted 15 July , 2004 Share Posted 15 July , 2004 Quote:-This being the heght of the Gun position and the height of the target in the horizontal plane, John, do you mean in the vertical plane? I`m struggling to work it out, otherwise! Link to comment Share on other sites More sharing options...
johnreed Posted 15 July , 2004 Share Posted 15 July , 2004 What might be confusing is that the heights are measured in a horizontal plane. The Mean Datum Plane for all heights in Europe is Amsterdam which is zero although height are vertical whether it be in elevation or depression it is still in the horizontal plane, and the only was is by using a bubble and that can be only measured in a horizontal plane. Is it less confusing now. John Link to comment Share on other sites More sharing options...
johnreed Posted 15 July , 2004 Share Posted 15 July , 2004 Ski Please find attached drawing. John Angle_of_Sight.doc Link to comment Share on other sites More sharing options...
Ski Posted 16 July , 2004 Author Share Posted 16 July , 2004 Mike, Phil, John, Thanks very much for your responces. I think i get the way it works now. Has anyone seen one of these objects before and do we think it is military, i.e could such and instrument be used in a building capacity or surveying? Thanks again, Ski Link to comment Share on other sites More sharing options...
johnreed Posted 16 July , 2004 Share Posted 16 July , 2004 Ski Yes it was military and it was used for finding angles of sight with reasonable accuracy from positions to which it is not convenient to carry a larger instrument on a stand. You must realize the all targets engaged by 13 pdr and 18pdr were direct fire engagements i.e. they could see their target that they were engaging. Regards John (A gunner of 27 years service) Link to comment Share on other sites More sharing options...
Ski Posted 16 July , 2004 Author Share Posted 16 July , 2004 Thanks again John, I'm certainley not going to doubt a Gunner of 27 years service!! Thanks, Ski Link to comment Share on other sites More sharing options...
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