The plate of the lastrometer consists of a rectangle of thin aluminum two and half inches wide by four inches deep. Half an inch from the top edge three slits should be cut in the metal so that a portion of a magnetized knitting needle three inches long may be threaded through the breadth of the plate, projecting half an inch on each side. This needle forms a cross bar at the top of the plate and should be accurately adjusted so that the broad surface of the plate is always in the same plane as the axis of the needle. To the projecting ends of the needle is secured a loop of copper wire four inches long whose other end is made fast to the other end of the needle and whose centre passes over the hooked end of the wire through the cork. The plate thus swings like a miniature signboard suspended from the hook. The surface of one side of the plate is now painted with several successive layers of a saturated solution of gum arabic in one ounce of water to which has been added one and a half drachms of luminous zinc sulphide or Sidot’s preparation (preferably the latter) and one liquid drachm of a ten per cent. solution of barium platino-cyanide. The other side of the plate should be painted with “optical black” or any other suitable dead black varnish. Between the edge of the bung and the central wire should be inserted at convenient intervals three or four sections of glass tubing whose internal bore exceeds half an inch. These serve to admit external influences to the interior of the lastrometer. When complete it will be found that the plate of the lastrometer is highly fluorescent and can be energized into greater activity by exposure to sun or artificial light. It is desirable that the plate should be kept in a state of relatively low radiancy, as otherwise spirit agency cannot raise its luminous powers to a higher degree. At a séance the instrument should be placed within the circle and the jar rotated till the magnetized needle can oscillate freely in its natural position pointing toward the North and South Poles. Concentrations of genuine spirit force will raise the luminosity of the plate to double and treble its normal output of light. When the force is concentrated in the lastrometer, questions can be answered by the spirits by signaling in Morse or simple code by rotating the plate through an angle of 90° against the surface force of the magnet.[11] It may be urged that this apparatus is not fraud-proof and that it would respond to certain agencies such as the concealment of an electromagnet in the room. To this it may be answered that an ordinary pocket compass placed on the table by the lastrometer would also respond to these forces and the fraud would be transparent to any observer.