Article 3 - Bias

ARTICLE 3 - Bias

(Originally published in 1997 and revised in 2009 & 2019)

Bias The Oxford English Dictionary considers the first use of the word, as follows "Originally an adjective, as in PR. "Via Biayssa" - cross or oblique road". The seamstresses amongst you will also recognise the use "on the bias" -being "diagonally, across the textures". The dictionary does say that the word became the technical term at the game of bowls, whence comes all the latter uses of the word.

So we can see that 'bias' comes from the bowl running obliquely to the line on which it was delivered. Again, referring to the Oxford English Dictionary, there are two very good paragraphs which are worth bringing to this article. They are as follows "a term of bowls applied a like to : the construction or form of the bowl in parting an oblique motion..... thus a bowl is said to have a wide or narrow bias. The second makes mention as follows "formally bias was given by loading the bowls on one side with lead and this was itself sometimes called the bias..... ..... they are now made of very heavy wood and the bias given entirely by the shape, which is that of a sphere slightly flattened on one side and protuberant on the other, as if composed of the halves of an oblate and prolate spheroid".

Well that has helped my education !!! but I wonder about the artificial weighting - certainly the story about the Duke of Suffolk's experience in 1522, may support it. Although, I always understood the significance of the story of when he discovered that his hastily cut bowl from the bannister post, having bias was thus able to "go round" the blocking bowls and giving him an advantage. I feel indicating that the other opponents bowls actually ran straight, not having bias introduced by another means..

Just a note, all artificial weighting is illegal - despite this when bowls come in for service, there are still some bowls that people have tried to 'adjust' the bias with loading.

The simplest way to show the bias effect and produce same is to take a snooker ball and produce a flat on one face and then run that ball on the table. Such a ball rolled along the table will turn away from the ''flatten" side, (just as for the Duke of Suffolk) and you have thus produced a biassed ball. Basically the side which has been ''flatten" is now lighter than the other side so the ball falls to the heavier side - the centre of gravity of the ball has been shifted from the centre of the ball.

This the simplest method of producing bias as described, obviously has to be modified for the production of a bowl so that the bowl can be comfortably handled.

Originally, with Lignum Vitae, (wooden) bowls the shift in the centre of gravity, used to produce the bias was more easily seen by the bowler. The reason being that as the timber is has a specific gravity of about 1.32 it needs a larger percentage of its mass to be 'off centre' to produce the bias. The more modern phenolic bowls using higher specific gravity material than Lignum Vitae means that that shift in the centre of gravity is visually less obvious, but is still there nevertheless.

 A3_bias _1

However, the bias can also be produced by adjusting the running sole, and any of you that have had your bowls adjusted will know that this in the method used to produce a change in a bowl to a required bias. At the Drake Pride factory, because we renovate large numbers of Lignum Vitae bowls (for the Crown Green players) where basically every set has to be re-biassed during renovation procedures, we therefore, have great experience and skill in the intricacies of hand biasing. However, as we now are producing the modern phenolic bowls on computer controlled lathes, it means that another set of skills is required to ensure that the bowls run as the manufacturer requires.

In 2019 Jean and Maurice Roger of Pershore Bowls Centre donated several items to the Bowls Heritage Collection. Amongst the items Was a booklet published by Taylor-Rolph in 1938. In the booklet was an interesting article - titled "What is Bias"
It is worth reading so a copy is below:-


A rather technical article, but worth reading because it shows you why bowls behave as they do on the green, and how the draw of any given bowl is determined.
"Bias: a technical term of the game of bowls, whence came all the later uses of the word. Origin unknown."
    So says the dictionary, but here it is necessary to amplify this terse definition. Bias is given to a bowl, not by any form of loading but entirely by its shape, which is that of a sphere having one side slightly flattened and the other protruding. This peculiar shape displaces the centre of gravity from the centre line, causing the bowl, when rolled upon a flat surface, to take a curved path during its progress.
    The degree of bias is determined by the extent of the displacement of the centre of gravity, or the inclination of the axis (from plate to plate of the bowl) caused by the displacement. The gyroscopic action of the moving bowl bowl resists this inclination, which imparts a turing movement to the bowl. It is this that causes the bowl to move in a curved path. The curvature of the path increases as the bowl loses speed and come to rest.
    Reference to the diagram will explain the behaviour of a bowl in play. A is the point of delivery and B the point at which the bowl comes to rest. The area bounded by the straight and curved lines is known as the amount of 'land' taken by a given bowl, in a given length, on a given surface.

Bias 1938    A light weight bowl requires more initial velocity and takes more 'land' to reach its destination than a heavy bowl. Apart from any unevenness or downward slope, the heavier and slower the green, the less 'land' will be taken by any particular bowl. The reason is that on a keen or fast green the contact between bowl and surface is very small. Friction is therefore less and the bowl will travel faster in its natural course than on a heavy green. The curve will be wider and consequently more 'land' will be taken.
    The draw of any given bowl in play is determined by the length B - C
over a given length A-B. A-C is the direction in which the bowl is delivered to reach the position of rest B.
    The draw of any given bowl in play is therefore governed by the nature of the surface upon which it is delivered. Provided the surface is the same, A-C will remain in ratio to A-B irrespective of its initial velocity.
    The behaviour of a bowl in play is determined by the weight, velocity of delivery, its bias (or displacement of the centre of gravity from the bowl's centre) and finally, by the nature of the surface upon which it is delivered.

The article "What is Bias?"was published by Taylor-Rolph in 1938

All manufacturers now use computer controlled. lathes (Drake Pride being the first company to install such equipment) and therefore the modern bowls no longer require hand biassing as the programmes that are used produce the 'total' geometric shape of the bowl. This may incorporate some shaping of the running sole, but all the shape is produced on the lathe, combining with the gravity shift and the mix of how these two basic methods are used is how the different manufacturers produce the different handling characteristics of their models.

From an interesting old book 'The Physics of Ball Games" there is a section on "the path of a a wood" across a bowling green, and this is worth producing as in relatively simple terms it does explain how the curved path of the bowl is produced.



Fig B.

The fact that a bowls 'wood' which has bias pursues a curved path across the green is a result of the principle of conservation of angular momentum, and its motion is best explained on that basis.

However, it is fairly easy to accept, at least in general terms, why it behaves as it does.

Fig. B is meant to represent such a wood, seen from above, rolling across a green in the direction of the arrow OA.

Since it is rolling, the top of the wood will be moving with a velocity in this same direction. Suppose the bias is on the right; that is to say, the centre of gravity of the wood Is to the right of its centre. Then this bias will tend to rotate the wood over from left to right, and so give the top of the wood a small velocity in the direction OB This, combined with the very much greater velocity along OA will give a combined velocity somewhat to the right of OA-along OC. It is therefore in this direction that the wood will tend to roll. In this way it will always tend to roll slightly to the right of the path on which it finds itself. In the early stages, when it is rolling rapidly forwards, the velocity along OA is very much greater than that along OB, and so the curvature of the path will be slight. Later on, as it slows down, the transverse velocity becomes relatively more important, and the curvature in the path gets greater and greater, until the bowl eventually stops rolling and comes to a halt.

In 2019 Jean & Maurice Rogers, the owners of Pershore Bowls Centre kindly donated to the Collection bowls items. One of which was a booklet title BOWLS published by The Taylor -Rolph Company Ltd. in 1938. In it was an article titkes 'What is Bias' and so we thought it worth adding to our 2017 article and is shown below :-

What Is Bias 1935

© Peter Clare 2019 - © E.A. Clare & Son Ltd. 2019 - reproduction of article allowed only with permission from E.A. Clare & Son Ltd.