There are many great contentions between miners concerning the forked twig, for some say that it is of the greatest use in discovering veins, and others deny it. Some of those who manipulate and use the twig, first cut a fork from a hazel bush with a knife, for this bush they consider more efficacious than any other for revealing the veins, especially if the hazel bush grows above a vein. Others use a different kind of twig for each metal, when they are seeking to discover the veins, for they employ hazel twigs for veins of silver; ash twigs for copper; pitch pine for lead and especially tin, and rods made of iron and steel for gold. All alike grasp the forks of the twig with their hands, clenching their fists, it being necessary that the clenched fingers should be held toward the sky in order that the twig should be raised at that end where the two branches meet. Then they wander hither and thither at random through mountainous regions. It is said that the moment they place their feet on a vein the twig immediately turns and twists, and so by its action discloses the vein; when they move their feet again and go away from that spot the twig becomes once more immobile.
Hildegard receiving the Light from Heaven (Wiesbaden Codex B, fo. 1 r)
Certainly Lana's project is impracticable: the learned Jesuit did not foresee that his empty copper balloons would be crushed by the external atmospheric pressure; but he nevertheless had a very clear idea and very remarkable for his time of the principle of aerial navigation by balloons lighter than the volume of air which they move. He ends his long chapter with some very curious considerations:
I do not see any other difficulties that can be opposed to this idea, except one which seems to me more important than all the others, and that God will not allow this invention to be ever successfully applied in practice, in order to prevent the consequences which would result from it for the civil and political government of men. Indeed, who does not see that there is no State which would be insured against a stroke of surprise, because this ship would be heading in a straight line on one of its strongholds, and, landing there, could descend there soldiers.
The attached engraving is the exact reproduction of the parachute that the author also defines in the following terms, certainly inspired by those of Leonardo da Vinci:
With a square veil stretched out with four equal poles and having tied four ropes to the four quinces, a man without danger will be able to throw himself from the top of a tower or some other prominent place; because although, at the hour, there is no wind, the effort of he who falls will bring wind which will hold back the sail, lest it fall violently, but gradually descend. The man therefore must measure himself with the size of the sail.
If Leonardo da Vinci's aerial flight experiments do not seem to have been carried out on a large scale, it is perhaps not the same with the parachute, the use of which is much safer. The description of Leonardo da Vinci was reproduced later, not without a notable improvement in the mode of representation of the apparatus, in a collection of machines, due to Fauste Veranzio and published in Venice in 1617.
Principle of the helicopter, drawing by Leonardo da Vinci
The examination of the original drawings of the great Italian artist is intersting. We reproduce by heliogravure a complete plate; it makes it possible to follow the thought which presided over its execution. We let Dr. Hureau de Villeneuve interpret it.
We see in the second row on the right a small character quite similar to a demon or a genie, for he wears a flame on his head and, next to this flame, a Latin cross. His arms end with the fingers of a bat. The figure is not yet finished when Leonardo already recognizes its insufficiency and, guessing the little muscular action of the arms, thinks of using the force of the legs. So we see a little higher, in the same plank, a vigorous man placed on his stomach, his legs bent and about to launch a violent kick. The protruding muscles, traced by an anatomist's pencil, reveal the great painter in an unassuming drawing.
An atom is the smallest particle of a chemical element. Two or more atoms come together to form a molecule: thus molecules form the mass of matter. A molecule of water is made up of two atoms of hydrogen and one atom of oxygen. Molecules of different substances, therefore, are of different sizes according to the number and kind of the particular atoms of which they are composed. A starch molecule contains no less than 25,000 atoms.
Molecules, of course, are invisible. The above diagram illustrates the comparative sizes of molecules.
This pictorial diagram illustrates the principal of Spectrum Analysis, showing how sunlight is decomposed into its primary colours. What we call white light is composed of seven different colours. The diagram is relieved of all detail which would unduly obscure the simple process by which a ray of light is broken up by a prism into different wave-lengths. The spectrum rays have been greatly magnified.