It is believed by the author that a classification and presentation of selected groups of the devices produced in the past by which it was by the inventor believed, self-motive power had been attained, will save much work in fields already thoroughly exploited.

So far as the author knows no book on the subject has appeared since 1870. The various encyclopedias published contain articles on the subject, but they are necessarily brief, and not satisfying to young men who have become interested ...

Copernicus, the astronomer, whose discoveries make him the great predecessor of Kepler and Newton, did not come from a noble family, as certain other early astronomers have done, for his father was a tradesman. Chroniclers are, however.

It would appear that the young Nicolaus, for such was his Christian name, received his education at home until such time as he was deemed sufficiently advanced to be sent to the University at Cracow. The education that he there obtained must have been in those...

The materials for the sketch of this astonishing man are sufficiently abundant. We make special use in this place of those charming letters which his daughter wrote to him from her convent home. More than a hundred of these have been preserved, and it may well be doubted whether any more beautiful and touching series of letters addressed to a parent by a dearly loved child have ever been written. An admirable account of this correspondence is contained in a little book entitled "The Private L...