Napiers work on logarithms greatly influenced the work that was to be done in the future. The logarithms ability to simplify calculations meant that Kepler and many others were able to find the relationships and formulas for motion of bodies. In turn, Keplers laws and observations provided a basis for Newtons theory of gravitation. Laplace commented that Kepler, by shortening the labours, doubled the life of the astronomer.
It can also be argued that logarithms were the early calculators and computers. Both of these things were invented to aid mathematicians in their calculations, exactly the same idea as the logarithm. Napier invented a primitive form of a calculating machine which is now called Napiers Bones. They consist of a set of rods which can be laid together to find the solutions to multiplications and divisions. A diagram of how Napiers Bones work (left) is from the Hutchinson Family Encylopedia.
( http://ebooks.whsmithonline.co.uk/ENCYCLOPEDIA/42/P0005342.htm).