Cannon sight question

[Enigma]

This is a 17th century gunner's level and sight:

How is this device used? I know that the plumb bob and angle to the right is for measuring the depression/ elevation of the cannon.

What I do not understand is the function of the extractable ruler to the left. My best guess is that it is a sight for the various pieces' calibers (12 pounder, 24 pounder etc) and that it probably was placed on the breech of the piece, but the exact function of this device eludes me. And how does the second scale "1, 2, 3 etc." fit in?

Can anyone provide me with more precise information?

 

How is this device used? I know that the plumb bob and angle to the right is for measuring the depression/ elevation of the cannon.

That would be a good guess, but actually the plomb and quadrant is to insure that the cannon tube is "on the level". Notice how the base of the device is arched to match the contour of the barrel. It would sit perpendicular to the length of the bore. Whereas a Quadrant measuring depression/ elevation would sit parallel to the length of the bore.

What I do not understand is the function of the extractable ruler to the left. My best guess is that it is a sight for the various pieces' calibers (12 pounder, 24 pounder etc) and that it probably was placed on the breech of the piece, but the exact function of this device eludes me. And how does the second scale "1, 2, 3 etc." fit in?

Actually, this would be a single calibre piece. the sliding scale is marked with the measured paces or whatever the national equivelent was of that day to yard or meter. 1 = 100, paces 2 = 200 paces, 3 = 300 paces and so on... It would not be marked in meters yet, as the metric system was first invented in 1790 by the French Academy, and this piece appears to be dated 1686. The holes would be aligned with a beaded front sight. This rear sight would be centered by means of aligning the pointer in the center of the cut outs you see in the base of the rear sight and the cannons vent.

Just a guess :grin:

CP

 

[robinghewitt]

"Arched foot with vertical rule containing sliding piece with multiple sighting holes; offset levelling arc with plummet and degree scale [0]-45."

Item 42501

They have a lot of old canoneer's kit in the Museum of History and Science at Oxford

Search their database for Gunner :thumbsup:

http://www.mhs.ox.ac.uk

 

[FireMaker]

:grin: I gots one. Reproduction that was made a few years ago - all brass. Use on my piece when we are at Fort de Chartres with live fire. Picked it up at a garage sale for not much.

 

Would love to see a photo of it!

CP

 

[FireMaker]

Looks just like the one above but shiney.

 

[mike alexandre]

Ok so whos going to make a couple of dozen of these for sale. I'd like the first one.

 

[Enigma]

Notice how the base of the device is arched to match the contour of the barrel. It would sit perpendicular to the length of the bore. Whereas a Quadrant measuring depression/ elevation would sit parallel to the length of the bore.

It is right that the plumb bob was probably used to ensure that the sight was at the highest point of the cannon's curvature, thus aligning it (albeit roughly) with the bore.

However, that would not explain the 0° to 45° markings on the arc scale.

But being that a cannon has the biggest range at 45°, the only logical explanation would be that the level was also used to determine the elevation by placing it lengthwise, with the arc pointing towards the cascabel to measure elevation or with the arc pointing towards the muzzle to measure depression.

I am, of course, aware that a period cannon could not be elevated or depressed that much (barring mortars), but this seems to me the only explanation for the rather big arc.

Also: The benefit of this sight, or so I have read, was that it could be operated exclusively from the back of the piece, whereas a quadrant had to be operated at the muzzle end, i.e. in the enemy line of fire.

 

However, that would not explain the 0° to 45° markings on the arc scale.

Actually Chuck :winking:, yes, it would explain why it stops at 45 degrees and not at 90. Any more than 45 degrees, and the piece would fall over on its side.

However, I won't preclude that an intelligent gunner couldn't or wouldn't have possibly thought to use it in the fashion that you are suggesting. It could have been squared true by aligning one side with the breech base. But seeing the thought that was placed in the design of the sight, it would follow that the maker would have also curved the sides of the base to match the contour of the barrel, as well.

CP

 

[robinghewitt]

There is no problem with it being used for elevation because this is the 17th century. The sight wasn't designed to be fixed to the gun, it was held in place for aiming and removed before firing. If you look at the base it has alignment marks not bolt holes.

It could check the cant, or, be turned 90 degrees to do the elevation :thumbsup:

 

I agree, that an intelligent gunner couldn't or wouldn't have possibly thought to use to check the piece's elevation.

The pointers, you highlight, are to center the sight by the pointer's alignment with the center of vent/touch hole.

However, there are no such witness marks on the sides of the base to ensure proper elevation measurement. Nor, are the sides of the base scalloped to match the contour of the barrel. So, with the thought that was placed in the design of the sight, wouldn't it follow that the maker would have also curved the sides of the base to match the contour of the barrel and marked it with pointers as well, to ensure an accurate reading? That's my thought.

CP

 

[Enigma]

Hello Claypipe,

not necessarily. Even if you have an offset of an entire inch to the left or right off the center line, you'd still get a fairly accurate reading of the elevation, given the eccentricity of bores in the 17th century. The reading would only deviate in tenths of degrees, which is accurate enough for those days.

 

Okay, now you've done it. Here's a pet peeve of mine. The notion that artillery of that time period was inaccurate.

Yes, in 1680, artillery was still in its teens, but it was far from inaccurate. I mean look at the instrument that started this discussion. And a quarter inch off at the start point multiples into yards and feet at the arrival point.

If these weapons were so poor, why did they replace the ballista, trebuchet and catapult?

CP

 

[Enigma]

I did not mean "inaccurate" as in "Oh dear, the artillery is so inaccurate that it deviated 90° from the target!" but as in "This cannon's bore is not quite centered, so that a measurement error of +/- .25° in elevation does not make that much of a difference."

 

[Powder Keg]

I think that the gun crews would quickly compinsate for a bore being off center. Just like we do with any modern firearm. If it shoots high and to the right we adjust our sights a bit.

 

[paulvallandigham]

Two points of observation. One: The width of the elevation sighting device, which is at 90 degrees to the base would allow someone behind the gun to sight the device so that it is positioned along the top edge of the gun barrel, held by a second man.

Two; The pendulum itself will tell the sighter if the device is canted, so there was no need to have witness marks on the barrel, or on the sides of the base of the device to do this job.

Elevtion was set either by pushing wedge blocks in and out, or later by turning an elevation screw under the barrel. As exacting as the screw could be, it was also slower, so you see it on land based cannons, and not on naval guns until the 19th century, I believe. Wedges are faster to adjust on a pitching gundeck. The sight allowed on to pick a stationary target to sight the gun on, and the sighting device was removed before the shot was fired. The officer in charge of the gun was usually given the task of both using the device, and maintaining it securely on his person.

There is another sighting, or elevation device that was used, that involved a pendulum that hung below the mouth of the barrel and was attached to a straight edged steel that was placed in the muzzle of the gun. The pendulum and protractor indicated level and the degree of elevation of the muzzle, regardless of the external demensions of the cannon, or whether the barrel was bored off center or not. I odn't know the history of these sighting devices, but I used one That I have described in shooting a British Light Six Pound Field Piece, and saw a similar device being used by a crew shooting a civil war vintage parrot gun. The sighting device used by that crew was pocket sized, and not like the one shown here at all.

 

Elevtion was set either by pushing wedge blocks in and out, or later by turning an elevation screw under the barrel. As exacting as the screw could be, it was also slower, so you see it on land based cannons, and not on naval guns until the 19th century, I believe. Wedges are faster to adjust on a pitching gundeck. The sight allowed on to pick a stationary target to sight the gun on, and the sighting device was removed before the shot was fired. The officer in charge of the gun was usually given the task of both using the device, and maintaining it securely on his person.

This is true of later pieces, but sixteenth century and earlier used other methods of Elevation

There is another sighting, or elevation device that was used, that involved a pendulum that hung below the mouth of the barrel and was attached to a straight edged steel that was placed in the muzzle of the gun. The pendulum and protractor indicated level and the degree of elevation of the muzzle, regardless of the external demensions of the cannon, or whether the barrel was bored off center or not. I odn't know the history of these sighting devices, but I used one That I have described in shooting a British Light Six Pound Field Piece, and saw a similar device being used by a crew shooting a civil war vintage parrot gun. The sighting device used by that crew was pocket sized, and not like the one shown here at all.

1537: Niccolò Tartaglia's gunner's Quadrant for aiming cannons, 1st firing tables.

This piece is a variation of Galileo's Compassio

CP

 

Here is a photo of the Franklin Mint piece that was being discussed. Click on it and a larger photo should come up.



Here's the instructions for it:

Franklin Mint's Gunner's Level
Instructions for Use
The Gunner's Level was designed to as-
sist the user of a large mounted gun or
cannon in "laying" his gun, that is, in
aiming it and correcting its elevation to
achieve an accurate shot.

To use the angle measurement, the
level was placed on the gun so the foot
(A)laid lengthwise on a plain part of the
barrel with the plumb bob (B) hanging
freely to indicate the angle of the barrel
on the curved scale (C).

If the shot, when fired, fell short,
for example, the angle of the gun could
be increased in a controlled way by
constantly consulting the level for a
coarse adjustment.

As the gunner drew closer to the de-
sired result, he would then turn the level
square to himself on the back end of the
gun straddled across the barrel. It could
then be effectively used as an adjustable
back sight to measure the elevation of
the gun by setting one of the instrument
sight holes (D) in line with the target.

The sight scale (D) has four holes to
suit the convenience and experience
of the gunner and make it possible to
use the sight over a considerable range
of elevations andd with a variety of guns.

They also state that this piece is offical issue of the National Maritime Historical Society and authenicated for historical accuracy, a precision calibrated scientific instrument.

CP

 

[Enigma]

Excellent! This is the information I've been looking for! I owe you one, Claypipe! :bow:

 

Excellent! This is the information I've been looking for! I owe you one, Claypipe! :bow:

No, Thank you for bringing this piece to my attention. In my book, we're even.

CP