Having a large mezzotinto with a frame and glass, (suppose of the king) take out the print and cut out a pannel of it, near two inches distant from the frame, all round. If the cut is through the picture it is not the worse. With thin paste or gum water fix the border that is cut off on the inside of the glass, pressing it smooth and close. Then fill up the vacancy, by gilding the glass well with leaf gold or brass. Gild likewise the inner edge of the back of the frame all round, except the top part. Make a communication between that gilding, and the gilding behind the glass; then put in the board, and that side is finished. Turn up the glass and gild the foreside exactly over the back gilding, and when it is dry paste on the pannel of the picture which has been cut out, observing to bring the corresponding parts of the picture and border together, by which it will appear of a piece, as at first (only part of it is behind the glass, and part before it.) Hold the picture horizontally by the top, and place a little moveable gilt crown upon the king’s head. If now the picture be moderately electrified, and another person take hold of the frame with one hand, so that the fingers may touch the inside gilding, and with the other hand endeavour to take off the crown, he will receive a terrible blow. If the picture were highly charged the consequences might be as fatal as those of high treason; for when the spark is taken through a quire of paper, and the discharge of the picture is made through it, a fair hole will be perceived in every sheet, (though a quire of paper, is thought a good armour against the push of a sword, or even against a pistol bullet,) and the crack exceedingly loud. The operator who holds the picture by the upper end, (where the inside of the picture is not gilt,) to prevent its falling, feels nothing of the shock, and may touch the face of the picture without danger, which he pretends is a test of his loyalty. If a ring of persons take the shock among them, the experiment is called “the conspirators.” _Colours changed by the Electric shock._ Mr. Cavallo accidentally observing that an electric spark, passing over the surface of a card painted red, marked it with a black stroke, was induced to try what would be the effect of sending shocks over cards painted with different colours; accordingly he painted several cards with different colours, and passed the discharge of a jar, containing about one foot of coated surface over them, the result of his experiments are the following— Vermilion was marked with a strong black track, about one tenth of an inch wide. The streak was generally single, but sometimes divided in the middle. Carmine received a faint and slender impression, of a purple colour. Verdigris was shook off from the surface of the card, except when it was mixed with a strong gum water, in which case it received a very faint impression.