PRCfCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 495 



there were Ihrec places in China noted for different kinds of carving. At 

 Ningpo they carve exclusively in wood, and at Amoy they are celebrated for 

 fine pit carving, such as those exhibited. They are really beautiful, the very 

 small figures and the various character of each pit is remarkable, every pit 

 having an entirely diff rent subject engraved on it. There is one that has 

 GOO faces carved on it. This is all done with three or four small steel gouges 

 and a bow-saw, such as watchmakers use. The work is done in the open 

 street ; twt) or three Chinese carvers will sit around a small table and make 

 these fine figures without using magnifying glasses. At Canton they work 

 in ivory only. 



Velocity of the Pistons of Steam Engines. 



Mr. "Watson said he had seen it stated in the English journals that they 

 were about constructing engines that would have a speed of 350 feet per min- 

 ute. That speed might be something new in England, but we have engines 

 in this country the pistons of which travel 750 feet per minute. Most of the 

 engines on the boats running on Long Island Sound make 500 feet. 



Tlic Chairniun read the fulluwing- items of scientific news.- 



A New Electro-Magnet. 



M. Cavlier, of Paris, has made an eUctro-magnet by means of a helix of 

 uncovered wire, which is stated by trustworthy experimenters to have 

 nearly three times the attractive power found in a magnet of similar size 

 in a coil of covered wire of equal length. The requisite condition to be 

 observed to obtain this eflect is that the different coats of wire shall be 

 separated by a sheet of paper, and that the exterior of the bobbins, whether 

 in wood or copper, shall be covered also with an isolating substance. 



Mr. Bartlett stated that Dr, John Bradley, of this city, some years ago 

 made helixes of uncovered wire. His magnets are so much sought after 

 that he cannot now supply his orders 



Suspended Magnetic Action. 



M. Plateau has treated, mathematically, the question of the suspending 

 of a magnetic needle in the air by ^he contrary action of two magnets, and 

 concludes that it is quite impossible to obtain such equilibrium, whatever 

 may be the number and distribution of the magnets. Thus the legend of 

 Mahocnet's coffin falls to the ground. 



On the Cause and Cure of Cataract. 



Sir David Brewster, while presiding at the late meeting of the Royal 

 Society of Edinburgh, stated that many years ago his attention had been 

 directed to this subject in consequence of having experienced an incipient 

 attack of this disease. Luminous bodies appeared surrounded by imper- 

 fectly triangular lines of light, some parts of which were deeply tinged 

 wi;h prismatic colors. He traced the cause of this disease to a deficiency 

 in the supply of the liquor morcjani in the crystaline lens, and its conse- 

 quent separation into laminse. The cure was effected in eight months by 

 copious and continuous 'doses of pulvis salinum compositum. He supposed 

 the supply of fluid to the crystaline lens might be derived from the aqueous 



