Science recognizes a vast spectrum of waves ranging from extremely short to very long wavelengths. On this band are light rays, radio, X-ray, infra-red ray, death ray, and ultra-violet ray, among others, which have been placed at the service of humanity. Between the known wavelengths, however, exist many whose use is unknown. It is with these “black gaps” that scientists today concern themselves.
Marconi, at the time of his death, was delving into the mysteries of one of them. Recently a black substance emitting a powerful and baffling ray was compounded by an eminent scientist and chemist.
Fastened in this wooden framework is a small portion of this substance or material which I have been fortunate in securing for purposes of demonstration.
“Please write two digits on this white card and hand it to me face down. — I will place it, still writing side down, under the framework for a moment, thus, and then lay it over here to one side. The ray has now not only penetrated the white card but has assimilated the value of the numbers written and will reproduce them on its upper surface. Do you see it forming — faintly of course? You can’t? Perhaps if I gave the ray more time to operate the result would be a clearer image. I’ll place the card under again. Now look! You still can not see anything? Just a moment. I’ll outline the figures for you with chalk. H-m-m, 17. What did you write? 9 and 8! Oh, yes, I neglected to mention that the ray adds the numbers written as well. Isn’t science wonderful?”
The simple and few requisites are a single pocket-size silicate slate (dealers have them as Vest Pocket Slates) with a flap made of white cardboard covered on one side with black paper. You also have a piece of white cardboard the same size as the flap, and a piece of white chalk. The flap is placed on the slate with the black side outward and the chalk is in the right trouser pocket.
The slate is casually shown on both sides during the patter and dropped lengthwise on the slightly curved left fingers which allows the flap to fall out. The right hand grasps the numbered card at edge and slides it under the end edge of the slate. A moment after it is out of sight the right fingers take the slate and card, pinching the latter against the frame, the left hand moving to the left which brings the flap into view. This makes a perfect switch. The flap is laid to one side.
The slate, with card clipped behind, is held vertically before the eyes of the spectator so that he can “see” the faint figures, and this action provides ample opportunity for reading the digits that he has written.
When the flap is placed under the slate for the second time it goes between the card and the slate. This is done easily because the card is clipped against the frame. The real numbered card then is laid to the right. Now the slate is held vertically before the spectator’s eyes once more, both sides being shown casually during the process. When the spectator is unsuccessful in reading the figures, the slate is passed to the right hand which is held with its back to the floor.
The slate is held with its side edge toward the floor and lying along the forefinger — the thumb being on the upper edge. As the left hand plunges into the pocket for chalk, the right hand tilts slightly towards the body and the flap falls into a perfect finger palm on the second and third joints of the middle and third fingers.
Now finding the chalk, the performer transfers the slate to the left hand and carries the palmed flap to the pocket from where the chalk is produced. All that remains is to mark the total of the two digits upon the slate and everything is ready for examination.
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