Makch 4, 1904.] 



SCIENCE. 



365 



of the theoretical velocity. The paper de- 

 scribes experiments to determine the con- 

 stants of Pitot tubes. Tubes with variously 

 formed tips and of inside diameters ranging 

 from .162 inch to .007 inch were placed in 

 the jet from an orifice in a thin plate. 

 Each tube gave a pressure practically the 

 same as that in the drum, from which the 

 water was flowing. No change was ob- 

 served when the tubes were moved back and 

 forth along the axis of the jet, the increase 

 of static pressure back of the plane of the 

 orifice exactly compensating for the dim- 

 inution of velocity pressure. To determine 

 the velocity of the jet, measurements were 

 taken of the coefficient of contraction, the 

 coefficient of discharge, and of the relative 

 velocities at different distances from the 

 axis of the jet. The mean velocity from a 

 two-inch orifice was found to differ from 

 that in the center by less than .0002. The 

 coefficients were : 



Coefficient of Coefficient of Coefficient of 



Orifice. Contraction. Disctiarge. Velocity. 



2 inch. .6162 .6112 .992 



1..5 inch .6115 .6119 1.001 



As the velocity was practically the same 

 in all parts of a section, the figures for the 

 coefficient of velocity represent the con- 

 stants of the Pitot tubes, which give read- 

 ings equal to the static pressure behind the 

 orifices. Similar measurements were made 

 with a short pipe from which the coefficient 

 of the Pitot was found to be .993." The 

 hydraulic micrometer caliper described in 

 the preceding paper was used in making 

 the above measurements. 



Professor J. Burkitt Webb, of Stevens 

 Institute, Hoboken, N. J., presented a 

 paper on 'Molecular Velocities,' in which 

 he offered a simple illustration in sup- 

 port of Maxwell's theoiy that the only 

 permanent state for the molecules is one 

 in which the velocities are not the same 

 for all molecules, but that all possible 



velocities must be supposed arranged ac- 

 cording to the law of probabilities. ' ' Sup- 

 pose a number of small elastic spheres of 

 equal mass moving in all directions with 

 equal velocities, and consider two of them 

 moving at right angles to each other, and 

 so that sphere B strikes sphere A at the 

 instant that the center of A crosses the path 

 of B, the velocity of A in the direction of 

 B's motion is zero, and therefore all of B's 

 motion will be transferred to A. This will 

 increase the velocity of A from v to v y'2 

 Evidently another rectangular blow from 

 a sphere C would increase this velocity to 

 ^l/ 3, and so on, so that we have in this a 

 proof that an equal distribution of veloci- 

 ties would not be a permanent one, and 

 that the final permanent distribution must 

 depend upon the possibilities of the various 

 phases of collision that may occur." 



Professor G. W. Bissell, of Iowa State 

 College, Ames, Iowa, presented a paper on 

 'Iowa Coals.' He stated that the Iowa 

 coal fields have an area of 20,000 square 

 miles, and include the southwest one third 

 of the state. The Des Moines valley mines 

 are the most active. In this district coal 

 is found at depths of from 100 to 300 feet 

 in veins from 18 inches thick and upwards. 

 The thinner veins are profitably worked in 

 conjunction with the manufacture of brick 

 and other clay products made from the coal 

 shales. Iowa coals are mostly bituminous 

 and non-coking. The average proximate 

 analysis gives: 



Moisture 8.08 



Fixed carbon 45.60 



Volatile 38.14 



Ash 8.18 100.00 



Sulphur 3.42 



The calorific power of Iowa coals as de- 

 termined at Iowa State College with the 

 Parr calorimeter ranges from 9,180 to 

 13,141, with an average of 11,780 B. T. U. 

 per pound of oven-dried coal. From a 



