638 State Board of Agriculture, &c. 



inches, is laid on the head of the stone, and a weight is laid 

 upon it to prevent its moving during blasting. There 

 is now exposed to the action of the blast, the marble sur- 

 face not covered by the iron letters within the outlines of 

 this shield. 



All being ready, tlie steam is turned on, and by a driving 

 pulley on the main shaft of the engine, the gun in motion 

 is carried across the face of the shield, and at the same time 

 the slab moves along gradually under the blast. Tlie sand has 

 hitherto remained in the little funnel, there not being pres- 

 sure enough to force it down, but the moment the steam is 

 turned on the gun, it sucks down, so to speak, the sand into 

 the sand cylinder, and the sand and steam meeting at a 

 point below where the steam enters, are both forced down 

 upon the exposed marble face. The work now performed 

 is a mechanical one. Every grain of sand is a miniature 

 chisel, cutting out a particle of marble, at the rate, perhaps, 

 of a hundred thousand particles a second, and as the slab 

 moves slowly along, bringing successive surfaces beneath 

 this cutting process, the face of the slab soon becomes cut 

 out, to a greater or less degree, everywhere except beneath 

 the letters and tlie outline shield. 



After about four minutes the slab will liave moved up as 

 far as the required length of the shield, the steam is turned 

 off, and the machinery stopped. The slab is now taken 

 into the mill, and the letters blown off by a little jet of 

 steam ; the stone is washed off, and piled on the platform 

 ready for slapping. 



As with all_ other new inventions, there have been defects 

 to overcome, and many o]>stacles to remove. It took Prof. 



