Processes in the Useful Arts. 349 



wish AB to revolve in twelve hours, then R must have eight teeth, and 

 O 96, or R 10 and O 120. If AB is to revolye in one hour, then R and 

 O must have the same number of teeth. Bull, des Sc, Technol. Jan. 1825, 

 p. 42. 



10. On the Construction of Chimneys. 



Mr Tredgold, in his work on warming and ventilating apartments, has 

 given the following rule for proportioning the upper orifices of chimneys 

 to their heights and the magnitude of the fire-places : 



Multiply by 17 the length of the fire-place in inches. Divide the pro- 

 duct by the square root of the height in feet, and the chimney above the 

 fire. The quotient will be the area of the upper orifice in square inches. 



Thus, if the fire is 15 inches wide, and the height of the chimney be 



17 X 15 

 9 feet, we shall have =36j square inches nearly, which is a rectangle 



of 6 X 6 inches, in a circle of nearly 7 inches in diameter. In chimneys 

 already existing, the upper orifices may be contracted to their proper size 

 by Parker's cement. The contraction of the lower end of the vent above 

 the fire should be nearly the same as the upper orifice ; and the throat or 

 lowest opening should not exceed the length of the bars. The length of 

 the front of the fire should be an inch for every foot of the room's length, 

 and the depth one-half the length. If the length of the chamber should 

 be such as to require a grate more than 30 inches long, two fire-places 

 should be constructed. 



11. M. Ventau's Gigantic Meteorological Eolian Harp. 



Captain Haas of Basle has designated by these names, an apparatus 

 which emits of itself a variety of sounds during a change of weather. 

 Since the year 1787, he had stretched above his garden fifteen iron wires, 

 320 feet long, and at the distance of about two inches from one another ; 

 the largest wire two lines in diameter, the smallest one line, and those of 

 intermediate size one and a half line. They were situated towards the 

 south, and are inclined 20° or 30° to the horizon, being stretched by 

 means of rollers properly arranged for the purpose. Whenever the wea- 

 ther changes, these wires sound with such loudness, that it is im- 

 possible to go on with a concert in the house. The sounds sometimes re- 

 sembled the hissing noise of water rapid in ebullition, sometimes that of a 

 harmonicon, and sometimes that of a distant chime, or an organ. 



The inventor of this curious apparatus is M. Ventau, provost at Burkli, 

 not far from Basle. He sometimes shot at a mark from his window ; and 

 in order that he might not go to the mark after each shot, he attached to 

 it a long iron wire to draw it to him at pleasure. He remarked more 

 than once, that that wire sounded exactly an octave ; and he found that 

 every iron wire, stretched in a direction parallel to the sounds, emitted 

 this tone at every change of weather. 



A brass wire did not produce any sound, nor did an iron wire, when it 

 was stretched from east to we3t. 



