MECHANICS AND USEFUL ARTS. Ill 



weight to be lifted will not be less, including friction, than from three to 

 four tons; and the time required for the operation will be at least five 

 hours. The expense, therefore, if done by hand, will be a considerable 

 item. The use of a small steam-engine has been suggested. 



GLAZED WATERPROOF CLOTH. 



A patent has lately been taken out in England for making waterproof 

 glazed cloth, to imitate leather, by the following process : About three 

 ounces each of litharge, brown umber and hydro-protoxide of manganese, 

 are subjected slowly to a boiling action in one gallon of linseed oil, for 

 about three hours. It is now spread over the surface of twilled cotton cloth 

 laid on a table, with a sponge, and then hung up in a warm room to dry. 

 After this, it is subjected to a second coat of the same oil varnish, rendered 

 black with lampblack. A small scraper is employed to put on the second 

 coat, as it is a little thicker than the first. If the varnish is desired to dry 

 quick, it is thinned with turpentine. When the second coat is dry, the cloth 

 is polished with pumice stone and water, to render its surface smooth and 

 close. Several coats of this varnish are put on in a similar manner, each 

 being dried before the other is applied. The finishing, or top varnish, is 

 made of linseed oil boiled with umber, litharge and Prussian blue, thinned 

 with turpentine. The finishing operation is running the cloth between two 

 engraved metal rollers. 



IMPROVEMENT IN MUSICAL INSTRUMENTS. 



A patent has lately been taken out in England, by J. Robertson, for an 

 invention which relates to a most simple method of increasing the volume 

 and richness of tone of musical instruments. As applied to violins or simi- 

 lar stringed instruments, the sounding-board is made somewhat thicker than 

 those in common use, and the inside is "deeply grooved, longitudinally, in 

 parallel lines. The grooving operation removes the white fibreless wood, 

 leaving the more fibrous portion standing. The back of the instrument 

 may also be grooved; but the sounding-board is the most essential feature 

 of the improvement. The sounding-boards, and their supports, of piano- 

 fortes may be grooved in a similar manner, and with good results. The 

 grooves leave the spaces of wood between them in such relative positions, 

 that an increased resonant vibratory action is thereby caused, which thus 

 greatly improves the tone of the instrument. Scientific American. 



ENGRAVING OF ROLLERS FOR CALICO-PRINTING. 







A Providence correspondent of the Boston Journal states that a mechani- 

 cal arrangement has been invented by Mr. Milton Whipple, and improved 

 by Mr. Thomas Hope, of Providence, by which the engraving of rollers 

 used in printing calicos and delaines can be accomplished " in one-quarter 

 the time formerly employed, and a great reduction of labor and expense. 

 The surface of the copper rollers are covered with three coats of asphaltum 

 paint before being placed on the machine. The mechanism is so arranged 

 that upon tracing an index figure, which only requires one person to attend 

 upon the sketch or pattern to be engraved, it forms a connection with several 

 diamond points placed above the roller, and causes them to move in the 

 same manner with the index. They thus scratch the lines of the pattern 



