228 Miscellaneous Intelligence, 



time, he takes it out, and draws and extends it between his hands 

 till it becomes exceedingly thin, thinner, perhaps, than the finest 

 paper. In this state it is laid on the article to be varnished, and 

 to which it adheres. When used with gold and silver leaf, as is 

 often the case, the gold or silver is placed between two folds of the 

 varnish, and thus applied : the fold on the inside is to make the 

 whole adhere, and that on the outside is to varnish and protect the 

 gold and silver, which shine through, and produce a good effect. 

 The varnish combines readily with various colouring substances, 

 which the people there use with it. — Trans. Soc. ArtSy xliv. 192. 



II. Chemical Science. 



1. Heat evoloedfrom Air by Compression. — By a mathematical 

 investigation of the heat extricated from air, when it undergoes a 

 given condensation, and by a reference to the experiments of Cle- 

 ment, Gay-Lussac, and others, Mr. Ivory finds, that " the heat 

 extricated from air, when it undergoes a given condensation, is equal 

 to three-eighths of the diminution ^temperature required to produce 

 the same condensation, the pressure being constant!^ Air, under a 

 constant pressure, diminishes l-480th of its volume*, for every 

 degree of depression on Fahrenheit's scale ; and therefore one 

 degree of heat will be extricated from air, when it undergoes a con- 

 densation equal to T-ku X4- ^xl-o-. If a mass of air were suddenly 

 reduced to half its bulk, the heat evolved would be -^ -r- -riir = 90°, 

 ^Phil. Mag. N. S. i. 89. 



2. On the Action of a Moving Metallic Disc, upon a portion of a 

 Voltaic Conductor. — Immediately after the highly interesting dis- 

 covery made by M. Arago, relative to the efl^ects produced recipro- 

 cally by magnets and metallic plates, when the one or the other 

 were put into a state of motion, M. Ampere was led by his views 

 of the nature of magnetism, to look for a similar effect, when the 

 magnet was removed and replaced by a conducting wire formed 

 into a helix, for when an electric current is sent through such a wire, 

 it is found to possess all the properties of a magnet. A double 

 spiral was formed from wire, and delicately suspended above a ho- 

 rizontal disc of copper, to which a rotary motion was given by 

 convenient apparatus, also of copper. The two extremities of the 

 wire forming the helix were plunged into two circular cups, or 

 troughs, filled with mercury, and placed in communication with the 

 poles of a voltaic battery ; a screen was placed between the copper- 

 plate and the suspended spiral. Immediately upon moving the 

 plate, the spiral began to turn in the same direction, precisely like 

 a magnetic bar, or like the assemblage of two vertical magnets 

 attached to a horizontal lever. Ultimately the rotary movement 

 became accelerated and continuous. Upon altering the direction 



* At 32° F,— Ed. 



