This is very beautifully shown by a simple experiment, which equally well illustrates the method by which mind influences mind. If a plate of glass is strewn with sand, and, while held in a horizontal position, a bow drawn across its edge, a musical sound will be produced from the vibration of the plate, and the sand, by the impulse, forms into various geometric lines, according to the note produced--each note giving rise to a figure peculiar to itself. So invariably is this the case that a piece of music might be accurately written from the forms assumed by the sand. Now, if a piece of parchment or paper be stretched, with proper precautions, across the top of a large bell glass and strewn with sand, and the glass plate held over it horizontally, and the bow drawn across its edge, the forms assumed by the sand on the paper will accurately correspond with the forms on the glass. If the glass is slowly removed to greater and greater distances, the correspondence will continue until the distance becomes too great for the air to transmit the vibrations. When a slow air is played on a flute near this apparatus, each note calls up a particular form in the sand, which the next note effaces and establishes its own. The motion of the sand will even detect sounds that are inaudible. Professor Wheaton devised a means of beautifully illustrating this sympathy. If a sounding board is placed so as to resound to all the instruments of the orchestra, and connected by a metallic rod of considerable length with the sounding-board of a harp or piano, the instrument will accurately repeat the notes transmitted. The nervous system, in its two-fold relation to the physical and spiritual being, is inconceivably more finely organized than the most perfect musical instrument, and is possessed of finer sensitiveness. But it must not be inferred that all minds are receptive. Light falls on all substances alike, but is very differently affected. One class of bodies absorbs all but the yellow rays; another, all but the blue; another, all but the red, because these substances are so organized that they respond only to waves of the colors reflected.