This is an adjustable arm made of brass. The base of the device is fixed to a table or other stable work surface. At the upper end, an optical body such, as mirrors can be hung (not here) which is used to copy enlarged/reduced drawings or paintings. The artist or engineer adjusts the arm so that the original and the enlargement/reduction could be seen simultaneously on the new page and the desired result drawn. (Today, this role is played by a camera/printer). Made in Paris at the end of the 19th century.