How to capture image from four cameras when you have only three usb ports in the laptop using C# and Emgucv?

Question

I am trying to get images from different cameras using capture class. I have three ports in the laptop but i have to use four cameras or may be more . I am using a usb hub and connecting the camera with it but it isn't working.

Capture capture1 = new Capture(0);
    Capture capture2 = new Capture(1);
    Capture capture3 = new Capture(2);
    Capture capture4 = new Capture(3);

But it is giving an exception of Couldnot capture from camera 3 ! Please help.