Read xml file attributes within two elements

I have the following xml file and I am trying to get the attribute value which is inside two elements.

XML:

<Processing>
      <Aggregation method="summation"/>
      <Interpolation method="linear" />
</Processing>

C#:

XmlDocument doc = new XmlDocument();
doc.Load(xmlFile);
XmlNodeList elemNode = doc.GetElementsByTagName(Aggregation );
for (int y = 0; y < elemNode.Count; y++)
    result = elemNode[y].Attributes[method].Value;

The following code return an empty string instead of summation.