PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 561 



" I suppose that tlie current of warm air had struck against the center 

 of the plate, slightly expanding it, and thus increasing the tension of the 

 rim sufficiently to overcome the tenacity of the metal. This diagram ex- 

 hibits the form of the crack. When the pieces are in contact in the center 

 they are considerably separated at the edges." 



Effect of Cast Iron on Wrought Iron. 



In the course of his remarks, Mr. Wiard said: " It is well known that a 

 half-inch rod of the most fibrous iron, by being dipped endwise into a ves- 

 sel of molten cast iron, has its fiber entirely destroyed, while if it is dipped 



in sideways the fiber is not injured." 



» 



Defects of Solid Wrought Iron Guns. 



" The contraction of the metal in cooling offers an insurmountable obsta- 

 cle to the construction of cannon of large caliber by the process of forging 

 solid. As the outside cools and hardens first it forms an unyielding hoop, 

 and when the interior cools and shrinks it must be pulled asunder, forming 

 fissures. These fissures are generally formed at the welds. Where the 

 welds are across the piece, as in the Ames gun, the fissures will run around 

 the bore. I saw in Washington the wax mold of the bore of the Ames 

 gun taken before it had ever been fired, and the grooves around the bore 

 were as large as my finger." 



Hardening Wrought with Cast Iron. 



Dr. Parmelee remarked that wrought iron may be case-hardened by dip- 

 ping it in molten cast iron. Horse shoes are hardened in this way in large 

 quantities. 



Musical Instruments. 



In discussing this subject some interesting facts were stated by Mr. May- 

 nard regarding improvements in the brass instruments used in military 

 bands. The Chairman having stated that the so-called saxe-horn was first 

 made and used in this country — the peculiarity of that class of instruments 

 being the construction <^if the rotary valve, invented by Robert Kerrison, 

 of New York city, by means of which the passage of the air is lengthened 

 or diminished, Mr. Maynard said that Mr. Allen Dodworth, of this city, first 

 turned the mouth or flaring end of the horn backward, so that the sound 

 would be heard more distinctly by the soldiers who followed. 



Tlio following statements were made regarding 



THE CYCLOID PIANOFORTE. 



There is no article of home luxury to the improvement of whicli such 

 earnest attention and such costly experiments have been directed as to the 

 pianoforte. During tlie past twenty years great changes have taken place 

 in the internal construction of the instrument, especially as regards the 

 scale, which has been enlarged so as to admit of a greater length of string. 

 The instrument is now strung with heavier wire, an increase of nearly 



[Am. I.vst.] J* 



