236 Progress of Invention. 



however, puts an end at once to all these inconveniences. ISTot only- 

 does the uranium-collodion contain so little of the silver salt as to 

 be perfectly harmless ; but, when the picture has been obtained, the 

 collodion may be removed, by means of soft cotton dipped in ether, 

 and the image will be found on the surface of the wood as distinct 

 as, and infinitely more perfect than, if it had been produced by the 

 pencil. 



A Simple Clock. — Clocks have, long ago, been constructed 

 which were capable of going for a very considerable time with one 

 winding up. But they have been found objectionable, from 

 their great weight, complication, and costliness. A clock was pre- 

 sented to the Society of Natural Sciences, at Versailles, which it is 

 stated will go without winding for a - year, or even a longer period, 

 and yet is liable to none of these objections. The only difference 

 between it and an ordinary clock is stated to be, the replacement of 

 the pendulum by a horizontal lever, which is made to oscillate by 

 the torsion of an elastic vertical wire. Varying the dimensions of 

 the lever, varies the rate of oscillation — that which was presented 

 to the Society vibrated once in six seconds. 



Self- Acting Apparatus fok Steering. — Electro-magnetism has 

 been already applied to purposes so varied and so numerous, that it 

 would be difficult to enumerate them. It has recently been pro- 

 posed to employ it in the steerage of ships. The idea is both novel 

 and ingenious, and, therefore, deserves attention, although, in its 

 present state, it can hardly be deemed either simple or reliable 

 enough, in practice, ' to secure the attainment of the object con- 

 templated. 



Dr. J. P. Joule proposes to attach to one end of a compound 

 system of needles, or magnetized bars, suspended with great deli- 

 cacy, a bent wire or commutator, one extremity of which will dip into 

 a central mercury cup, connected with one pole of a galvanic bat- 

 tery, and the other extremity into the one or the other of two con- 

 centric semicircular mercury troughs, which are, respectively, in 

 connection with two electro-magnets, and, through their helices, 

 with the other pole of the battery. "Which of the electro-magnets 

 will be excited will depend on the position of the ship at the time, 

 with reference to the plane of the magnetic meridian, as on this will 

 depend the mercury trough which, by means of the commutator, will 

 be brought in connection with the central mercury cup. Whichever 

 of the magnets happens to be excited, will attract an armature placed 

 between both of them : and this, by means of levers, will act on 

 valves, so as to cause steam to move a piston in one direction or the 

 opposite, as may be required, until the vessel shall have returned to 

 its proper course. It is obvious, however, that, were no other ob- 

 jection to suggest itself, in practice, the pitching and rolling of the 

 ship must be very likely to seriously interfere with the action of 

 such an apparatus. 



Photographic Enamelling. — M. Poitevin, to whom the Academy 

 of Sciences awarded the Tremont Prize, for his discoveries in litho- 

 photography, on the 6th of February last, had advanced, step by 



