or ARTS AND SCIENCES. 307 



Three hundred and sixth Meeting. 



March 7, 1848. — Monthly Meeting. 



The President in the Chair. 



The Corresponding Secretary read letters of acceptance 

 from the Hon. Capt. W. H. Smyth, President of the Astro- 

 nomical Society of London, and from Professor Spencer F. 

 Baird, of Carlisle College. 



Dr. M. Wyman, from the Committee, appointed at the Oc- 

 tober meeting, to make experiments for testing the value of 

 the principal kinds of ventilating apparatus now in use, made 

 a report, of which the following is an abstract. 



" The apparatus used in most of the following experiments consists, 

 1st, of a machine for producing and maintaining a constant and equable 

 blast of air; 2d, of an arrangement for measuring the velocity of the 

 current produced by this blast. 



" The air is put in motion by means of a revolving fan of four blades 

 or vanes, each 21 inches long by 10 inches wide, placed upon the ex- 

 tremities of radii 13 inches in length. These blades revolve within a 

 cylindrical case, nearly concentric with the axis of the blades, to which 

 the air gains admission by two circular openings 13 inches in diameter, 

 one in either end of the case. From one side of this case, the air, 

 put in motion by the blades, enters a trunk 3 feet in length, and at its 

 commencement 21 inches wide by 18 inches deep, which is gradually 

 contracted until, at its farther extremity, its cross section becomes a 

 square of 100 inches area. To the mouth of this trunk another is 

 fitted, also 10 inches by the side and 3 feet in length. This last was 

 added to avoid any interfering or unequal currents which might be 

 produced by the converging sides of the first. Upon the axis of the 

 blades is fixed a pinion of sixteen leaves, which engages a wheel of 

 eighty teeth, driven by a handle ; consequently the blades revolve 

 with five times the velocity of the handle, or 300 times per minute 

 when the handle makes one revolution per second. This is the ve- 

 locity always used in the following experiments, unless otherwise 

 stated. 



" To measure the velocity of the blast, a toy marble, .62 inch in 

 diameter, is suspended by a silken thread, to which it is fastened by a 

 little sealing-wax. This thread is 3 feet in length, and the point of 



