The apparatus is used to measure the linear dilation of metal rods, it is made of brass and lies on a large wooden base (62 x 21 cm, height 10 cm) with a drawer.
The metal rod the lengthening of which is to be determined is placed on two staffs over a seven-flame alcohol burner. One of the staffs has a zeroing screw and holds one of the ends of the rod; the other staff allows the other end of the rod to lengthen and press on the shortest arm of a lever. The longer arm terminates with the arc of a gear wheel which moves the pointer on a scale divided into 100 parts (each division equals 1/50 mm).