exc = WScript.CreateObject("Excel.Application");

function ....

  this.ai = new Array();
  this.at = new Array();
  ...
  this.wb = exc.Workbooks.Open("somefile.xls");
  this.ws = wb.Worksheets.Item( 1 );   

  this.ai = this.ws.Range(this.ws.Cells.Item( 1 , 2 ),    this.ws.Cells.Item( 99 ,    3 ));
  this.at = this.ws.Range(this.ws.Cells.Item( 100 , 2 ), this.ws.Cells.Item( 200 ,  3 )); 

...

  /*?*/  this.ai = this.ai.concat(this.at);