INK BOTTLE.--1. Mineralogists apply the term “pyrites” to a large group or family of minerals, compounds of metals with sulphur, or with arsenic, or with both. The name was originally given to the sulphuret of iron, known as iron pyrites, in consequence of its striking fire with steel (from the Greek _pyr_, fire), and it was used for kindling powder in the pans of muskets before gun-flints were introduced. Iron pyrites is commonly of a bright brass-yellow color, and is found crystallized in cubes, dodecahedrons and many other forms. It is a very widely diffused and plentiful mineral, and seems to belong almost equally to all geological formations. 2. Eagle cents issued in 1858 are of no value to collectors, because they lack rarity. 3. Your exchange is too trivial. J. B. D., of Chicago, kindly informs us that he has been able to get a slight shock from a telegraph battery in the following manner: “On every learner’s instrument there are two binding-posts, and to one of them is joined a wire from the battery; a small file is fastened to the other; the key is closed, and then the other wire of the battery is taken in your wet fingers, and, with the other hand, also wet, upon the file, the wire is run along the surface of the file, and a shock results.” WALTER R.--What is known as the registry system is intended to secure to valuable mail-matter in its transition through the mails the utmost security within the province of the Post Office Department. The fee on any registered matter, domestic or foreign, is fixed at ten cents on each parcel or letter, to be affixed in stamps, in addition to the postage. The money-order system is intended to promote public convenience, and to secure safety in the transfer through the mails of small sums of money. The rates may be ascertained by inquiring at a local office. AN ADMIRER OF G. D.--1. Two French scientists, Captain Renard and M. Tissaudier, have invented a balloon whose motive power is electricity. The dynamo machine used by them is an intensely concentrated bichromate battery of one and a half horse-power. It is very light, weighing but 121¼ pounds. Several successful experimental trips have been made in this machine, and the inventors claim that by using all the battery power, they were enabled to navigate against the wind. They may be over-sanguine, but expect, after making some improvements in the balloon, to attain a speed of from fifteen to twenty miles an hour. 2. Constant base-ball practice will harden the hands. No artificial preparation is used by professionals.