Fra Luca and Messer Galeotto Sacrobosco, whose cottage by the Porta Vercellina had been destroyed by the French, were both at the villa when Leonardo arrived; but he kept himself apart, preferring solitude. He conceived, however, a great fondness for the company of Francesco, his host's little son.

Timid and shy as a girl, the boy at first stood in great awe of the painter; one day, however, he came into his room at a moment when Leonardo, studying the laws of colour, was experimenting with coloured glass. He pleased the child by letting him look through the different pieces, yellow, blue, purple, or green, which gave a fairy aspect to familiar objects, and made the world seem now smiling, now frowning, according to the colour of the glass. Another of Leonardo's inventions proved very attractive. This was the 'Camera obscura,' by means of which living pictures appeared on a sheet of white paper; and Francesco saw the turning of the mill-wheel, the swallows circling round the church, the woodcutter's grey donkey with his load of faggots stepping daintily along the miry road while the poplars bowed their heads under the breeze. Still more fascinating was the weather-gauge: a copper ring, a small stick like the beam of a balance, and two little balls, the one covered with wax, the other with wadding. When the air was saturated with moisture the wadding grew heavy, and the little ball, falling down, inclined the beam till it touched one or other of the divisions marked on the copper ring. The degree of damp could thus be accurately measured, and the weather predicted for two or three days. The little boy constructed a similar apparatus for himself and was jubilant when the prophecies were fulfilled which he had deduced from its variations. Francesco went to the village school where he was taught by the old prior of the neighbour convent. The dog-eared Latin grammar and arithmetic primer were odious to him, and he learned but slackly. Leonardo's lore was of a new sort, pleasant to the child as a fairy tale. The instruments for the study of optics, acoustics, hydraulics, were to him new and magical toys, nor was he ever tired of hearing the painter's talk. Fearing ridicule or suspicion, Leonardo spoke but cautiously with adults; to Francesco he talked with the utmost frankness and simplicity. He not only taught the child, but learned of him. Paraphrasing the text of Holy Writ, he told himself—'Except ye be converted and become as little children, ye shall not enter into the kingdom of knowledge.'

It was at this time that he was writing his Book of the Stars. On March evenings, when in the still chilly air there was a waft of spring, he would stand on the roof with Francesco, watching the tide of stars and sketching the spots on the face of the moon. Then rolling a piece of paper into an inverted cone, he bade the child look through the aperture at the end, and Francesco saw the stars robbed of their rays, and like bright, round, infinitely minute globules.

'Those globules,' said Leonardo, 'are of great size, many of them a hundred, nay, a thousand times larger than our earth, which, however, is not less beautiful nor more contemptible than they. The mechanical laws which obtain in our world, and which have been discovered by human sagacity, guide also those stars and suns.'

'What is there beyond the stars?' murmured the child.

'More stars, Francesco; worlds which we cannot see.'

'And beyond those?'

'Yet others.'

'But at the end, at the very end?'

'There is no end.'