You are calling:
JSON.parse(scatterSeries)
But when you defined scatterSeries, you said:
var scatterSeries = [];
When you try to parse it as JSON it is converted to a string (""), which is empty, so you reach the end of the string before having any of the possible content of a JSON text.
scatterSeries is not JSON. Do not try to parse it as JSON.
data is not JSON either (getJSON will parse it as JSON automatically).
ch is JSON … but shouldn't be. You should just create a plain object in the first place:
var ch = {
"name": "graphe1",
"items": data.results[1]
};
scatterSeries.push(ch);
In short, for what you are doing, you shouldn't have JSON.parse anywhere in your code. The only place it should be is in the jQuery library itself.