Development of the idea of the Vector Cross Product

Engineering mathematics uses the vector dot product and cross product, often as mathematical definitions with useful properties. The dot product gives the vector amount that one vector contributes along the same line as another vector, and that straightforward result may serve as sufficient explanation for the dot product. The cross product, however, is partly the result of multiplying different components of two vectors to get a product vector that is at right angles to both of the original vectors and that has a magnitude equal to the area of the parallelogram that the two vectors frame. The reason for multiplying the components of the vectors in such a manner is usually not explained in terms of how the mathematics was designed to account for properties of nature. The usual explanation is that the mathematical relation will be found useful.

The dot product is

a · b = |a||b|cos(theta)

The magnitude of the vector cross product is

|a X b| = |a||b|sin(theta)

And the vector cross product is

a X b = (a2b3 - a3b2)i -(a1b3 - a3b1)j + (a1b2 - a2b1)k

The magnitude of the cross product is equivalent to the area of the parallelogram that the two vectors (a and b) describe, and the formula for the vector product is the same as the determinant for the array shown here.

    | i  j  k|
det |a1 a2 a3|
    |b1 b2 b3|

The vector product is perpendicular to both of the original vectors.

Cross Product

A few questions

While trying to find more about the origin of the cross product in particular, I found an advertisement for a book about determinants in a 1882 book about quaternions. The advertisement promoted the book as increasing interest in the discussion through showing how natural considerations led to the development of the determinant. More generally, it seems that including the historical development or even the cause for the development of a tool shows an appropriate use of the tool or property.


The following information is from A History of Vector Analysis; The Evolution of the Idea of a Vectorial System, Michael J. Crowe, 1967, republished in 1985.

Early influences

Creative Design
Sir William Rowan Hamilton (1805-)
Hermann Grassmann (1809-1877)
A History of Vector Analysis, James Walter Joiner, 1971, (doctoral dissertation at George Peabody College for Teachers)

The history of the development of vectors and the cross product involved more than one person and the consequent choices and practice of the community of workers who heard about and used the developing set of tools. Hamilton was one of the early developers, notably from his discovery of quaternions in 1843. His idea seems to have been based on analogies with the theory of complex or imaginary numbers (numbers having a component with a factor of the square root of -1.) Hamilton was the first to use the word vector, based on the Latin veher, "to draw".

Oliver Heaviside promoted the use of vectors (including cross products) in his 1893 book "Electromagnetic Theory". He said that vector mathematics were considerably easier to use than quaternions and that vector mathematics could be discovered while using Cartesian mathematics through noting groups of calculations that repeat when working with the math for certain kinds of engineering applications.