MECHANICS AND USEFUL ARTS. 105 



Improved Tunneling Machine. A very ingenious apparatus has been 

 devised to facilitate the progress of the Piedniontese railroads, in 

 which tunnels have to be cut under mountains. The excavating 

 machine cuts the channels in the rock, by means of several series of 

 chisels placed one beside the other, in straight lines ; these lines of 

 cutting tools are so arranged as to be capable* of a slight motion in the 

 direction of the grooves after every stroke ; the object of this is to 

 bring the chisels to bear upon all the spaces lying between the several 

 cutting tools situated in the same line, so as to produce not a succes- 

 sion of holes, but a continuous channel similar to a very wide saw-cut. 

 This lateral shifting of the lines of chisels, which takes place alternately 

 from right to left, and from left to right, is caused by a corresponding 

 motion given to the frames in which they are fixed. Each chisel is 

 driven against the rock by a spiral spring coiled round it. This spring, 

 driving the chisel forcibly against the rock, obliges it to act efficaciously, 

 notwithstanding the slight inequalities at the bottom of the channel, 

 arising from a want of uniformity in the resistance of the stone. When 

 the machine is in operation, the several lines of chisels are all drawn 

 back simultaneously, by means of a species of cam, or moveable bar. 

 The apparatus is arranged so as to enable each chisel to strike 150 

 blows in a minute. The machine at the same time sets in motion a 

 pump, which forces a constant supply of water into a reservoir, the 

 upper part of which is filled with compressed air. By this means the 

 water is driven out in jets, through small pipes placed between the 

 chisels, and is thus made to play upon the grooves, where it performs 

 the double office of preventing the cutting instruments from becoming 

 heated, and removing the dust and broken stone, which would other- 

 wise accumulate in the grooves, and thereby prevent the effectual 

 working of the excavator. 



IMPROVEMENTS IN MODELLING IN PLASTER. 



DURING the past year a patent has been granted to Hiram Powers, 

 the sculptor, for improved files, to be used in connection with certain 

 improvements in modelling, which he has lately invented. These 

 improvements are described as follows in a letter from the inventor to 

 the editors of Putnam's Magazine. 



The principal tools used in the work consist of chisels, scrapers, 

 and trowels, the blades of which are of gutta percha set in metallic 

 backs, and elastic, so that the plaster can be put on with them some- 

 what as with a brush, and perforated or open files every tooth hav- 

 ing an opening in front of it, through the body of the instrument, so 

 as to allow the dust and filings to pass through and escape, leaving the 

 teeth unclogged and free to act. The files are of various forms and 

 sizes, being curved, round, flat, &c. The material used is common 

 plaster of Paris. 



^ In projecting a human figure, a pair of irons, reaching nearly as 

 high as the hips, and corresponding in general direction to the bones 

 of the legs, must be set up on a platform, and around these a base 



