linked perlin noise to wikipedia

_tutorials/03_graphics/generativemesh.markdown

@@ -432,7 +432,7 @@ The mesh resembles something you might find under a microscope, so let's add som
 
 ![Jitter](003_images/jitterSmall.gif)
 
-On each frame, we are going to move each vertex by a small, random amount.  Instead of using [ofRandom()](http://www.openframeworks.cc/documentation/math/ofMath.html#show_ofRandom) to displace our vertices, we are going to use [ofSignedNoise()](http://openframeworks.cc/documentation/math/ofMath.html#!show_ofSignedNoise) which generates a thing called Perlin noise.  Check out Daniel Shiffman's description of Perlin noise in section [1.6 Perlin Noise (A Smoother Approach)](http://natureofcode.com/book/introduction/#i6-perlin-noise-a-smoother-approach) of his online book.  Perlin noise yields random values that smoothly vary over time.  You can get a good idea of the difference between random values and Perlin noise by checking out [figure 1.5](http://natureofcode.com/book/imgs/intro/intro_05.png) (which shows sequential values of noise) and [figure 1.6](http://natureofcode.com/book/imgs/intro/intro_06.png) (which shows sequential random values) from the book.
+On each frame, we are going to move each vertex by a small, random amount.  Instead of using [ofRandom()](http://www.openframeworks.cc/documentation/math/ofMath.html#show_ofRandom) to displace our vertices, we are going to use [ofSignedNoise()](http://openframeworks.cc/documentation/math/ofMath.html#!show_ofSignedNoise) which generates a thing called [Perlin noise](https://en.wikipedia.org/wiki/Perlin_noise).  Check out Daniel Shiffman's description of Perlin noise in section [1.6 Perlin Noise (A Smoother Approach)](http://natureofcode.com/book/introduction/#i6-perlin-noise-a-smoother-approach) of his online book.  Perlin noise yields random values that smoothly vary over time.  You can get a good idea of the difference between random values and Perlin noise by checking out [figure 1.5](http://natureofcode.com/book/imgs/intro/intro_05.png) (which shows sequential values of noise) and [figure 1.6](http://natureofcode.com/book/imgs/intro/intro_06.png) (which shows sequential random values) from the book.
 
 With ofRandom(), you specify a range of values, and it returns a random value within that range.  If you were to call it multiple times in a row, you will (very, very likely) get a new value every time you call it.  Perlin noise works a bit differently.  ofSignedNoise() will always return a value between -1.0 and 1.0, but you still have to pass in an input to the function.  Think of ofSignedNoise() as a squiggly line drawn on graph paper.  You pass in a coordinate, an x value, and it will return the corresponding y value.  If you were to call ofSignedNoise(3.0) multiple times, you would get the same value every time.