Pboceedings of the Polytechnic Association. 857 



Ml*. Emery said that it had been lately suggested to place revolv- 

 ing forts upon water, so that their easy rotation might be assured ; to 

 which Dr. Kicli replied that a model of precisely this character had 

 been for many years in possession of the American Institute. 



Rollers foe Calico Printing. 

 The Swiss calico printers save much of the cost of copper rollers 

 by substituting iron rollers, which are coated with copper of sufficient 

 thickness to receive the engraved pattern. When the pattern is worn 

 out or no longer fashionable, all the roller, except the engraved part, 

 is covered with an insulating varnish. On being immersed in an 

 electrotype bath, all the exposed portions are soon filled up with cop- 

 per, and the roller is then ready to receive a new pattern. The Swiss 

 process for coating iron rollers with copper is still a secret. Weis- 

 kopt has just devised the following : First brush the iron roller with 

 a solution of one part of nitrate of copper in fifty parts of hydrochlo- 

 ric acid. Then with a solution of ten parts of nitrate of copper, ten 

 of chloride of copper, and eighty of hydrochloric acid, applied quickly 

 with a soft brush. After being rinsed and wiped with a soft cloth, the 

 second solution is again applied, and so on until a sufficient thickness 

 of copper has been deposited. The process is cheap, and copper is 

 not apt to peel ofi if the solutions are applied very quickly. 



Electrical Piano. 



A musical instrument, more remarkable for its ingenious mechan- 

 ism than for its cheapness and availability, has been brought out by 

 M. Speiss, of Sumiswald, Switzerland. By means of clock-work, two 

 rollers are set in motion, which carry from one to the other a band 

 of strong paper, containing perforations like that used in a Jacquard 

 loom, and passing over an intermediate brass roller put in connection 

 with the wires of an electric battery, which are arranged in coils 

 around soft iron rods, and become magnets whenever the current of 

 eleptricity is. unbroken. The current is closed by means of a series 

 of pins touching the brass roller, and is broken when the paper 

 passes between them and the roller. Thus a series of iron fingers, 

 by being magnetized and demagnetized, are made to strike the keys 

 to a series of strings with astonishing rapidity. Besides the power 

 which moves the clock-work, a battery of thirty-six Daniel's elements 

 is required to operate this automatic instrument. The greatest diffi" 

 culty to be encountered is in giving the dynamic effijct from which 



