Polytechnic Association. 851 



On visiting the doctor's pleasant house, there, on the mantel-shelf 

 in his parlor, sat a bust of Webster, just as it came from the machine, 

 every feature perfect, and the life-like expression of the lion face 

 never excelled by any artist. Surely will mechanism compel the 

 sculptor to lay down his chisel. 



Dr. B. proceeded to explain the cutting point. It has been 

 hitherto supposed that a slow motion is required. On the contrary, 

 it is found that, when revolving forty or fifty revolutions per second, 

 its cutting property will be destroyed ; but revolving from seventy to 

 eighty revolutions per second, it will last indefinitely. Fine steel 

 may be made to retain its sharpness in the presence of quartz. 



The President — The principle involved is the same as in the Tilgh- 

 man Sand-blast, that a soft substance in rapid motion will cut a much 

 harder substance. Some years ago a wooden steamboat, the Swallow, 

 ran directly through one of our city piers, which was filled in with 

 stone ; and I learn from Dr. Blanchard, to whom I stated this to-day, 

 that it was one of the facts which led him to make his discovery. 



Dr. Blanchard — It was the great fact. 



The President — On the same principle a disk of copper may be 

 revolved so rapidly as to cut the hardest steel. The essential 

 improvements in this machine, over the lathe of Thomas Blanchard 

 (of whom the Dr. is a distant relative), is that the tool has a rapid 

 rotation. 



Dr. P. H. Van der Weyde — If the pier had been in motion and 

 the vessel Tstill, the result would have been the same. When the disc 

 of copper cuts the steel, it is not by its velocity, but because a great 

 many particles of copper come to act upon the same point. But in 

 the case of the vessel coming in contact with the pier, motion and 

 rest being only relative, it makes no difference which was in motion. 



The President — It is said, you can shoot a tallow candle through a 

 pine board. 



Dr. Yan der Weyde — For the same reason that a great many 

 particles follow each other to increase the effect produced by the 

 first. 



Mr. Keuben Bull described a similar machine which he had con- 

 structed in 1866. The tool revolved 8,000 times per minute. All 

 the works revolved on steel points ; there being thirty-two steel 

 points, connected with two sets of parallel levers. It required to be 

 guided by the thumb and finger in tracing, and was used for cutting 

 medallions, eight inches in diameter. 



Dr. Van der Weyde stated that a similar machine was used for 



