Page:Popular Science Monthly Volume 63.djvu/386

382 specimens of uraninite, or pitchblende, one from mines in Cornwall, and the other from Bohemia; as is well known to readers of the only a few decigrams of radium can be separated from a ton of the mineral, and the isolation of the element is difficult, owing to its chemical affinities with the metals of the alkaline earths (barium, strontium and calcium). In contrast with the velvety black, massive pitchblende, are a few decigrams of pure radium bromide, a white salt resembling exteriorly common salt. Near by is a salt of barium, the crystals of which are rendered luminous when exposed to the emanations from a radium compound, even when a pile of copper coins, or a piece of marble more than one inch in thickness, is placed between them. The labels on these specimens duly explain that these emanations also act in the dark on photographic plates, and make the air traversed by them conductive of electricity.

The exhibition also includes the following: A box blackened inside and mounted on a stand, the whole resembling somewhat a large photographic camera, especially since the open end of the box is screened with black velvet that might be mistaken for a focusing cloth. On raising this screen the visitor sees at the farther end in letters of light, the word R-A-D-I-U-M. This word has been painted with radium bromide on hexagonal sulphide of zinc, which becomes luminous when brought near a compound of radium. Thus the emission of light by the new element is demonstrated as effectively, though not so strikingly as by Sir William Crookes in his experiments at the conversazione of the Royal Society, when the scintillations of radium were rendered visible by means of a blende screen and intensified by the use of a lens of moderate magnifying power. Residents of London, and visitors to that metropolis, will enjoy forming practical acquaintance with radium and with some of its extraordinary properties that may be envied by citizens of America.

the meeting of the American Philosophical Society last spring, Mr. J. G. Rosengarten gave an account of some seventy large folio volumes of Franklin's papers, preserved in the archives of the society. Franklin left all his papers to his grandson, William Temple Franklin, who, after a long interval, published in London and in Philadelphia six volumes of Franklin's works. Of course, this represented but a small part of his papers. Those used in the preparation of Temple Franklin's edition are now the property of the United States, which has never yet printed a calendar of them. Temple Franklin selected from his grandfather's papers those that he thought suitable for publication, and left the rest of them in charge of his friend, Charles Fox, to whom he bequeathed them, and Charles Fox, in turn, after a long lapse of years, presented them to the American Philosophical Society, in whose custody they have remained ever since.

They have been roughly classified, and are bound in a rude and careless way. Under the present efficient librarian. Dr. Hays, a calendar is being made as fast as the limited means at his disposal will permit, and, when it is completed, it is hoped that it will be printed as a useful guide to the miscellaneous matter collected here. Sparks, Hale, Ford, Parton, Fisher and others who have written about Franklin have used them, but even the most industrious student may well be appalled at the labor required to master all the contents of these bulky volumes representing Franklin's long and many-sided activity.

He kept copies of most of his own letters and the originals addressed to him, often indorsing on them the heads