Apeil 9, 1897.] 



SCmNGE. 



573 



We see that the values obtained by actual 

 observation are alwaj's greater than those 

 obtained under the assumption that only 

 accidental causes influence the averages for 

 each class. We also see that these causes 

 reach a maximum during the period of 

 growth and decrease as the adult stage is 

 reached. The maximum is found in the 

 fourteenth year in the case of boys, in the 

 twelfth year in the case of girls, i. e., in 

 those years in which the effects of accelera- 

 tion and retardation of growth are strongest. 

 Although the values given here cannot 

 claim any very great weight on account of 

 the small number of classes, this phenom- 

 enon is brought out most clearly. 



The figures prove, therefore, that the 

 differences in development between various 

 social classes are, to a great extent, results 

 of acceleration and retardation of growth 

 which act in such a way that the social 

 groups which show higher values of meas- 

 urements do so on account of accelerated 

 growth, and that they cease to grow earlier 

 than those whose growth is in the beginning 

 less rapid, so that there is a tendency to 

 decreasing differences between these groups 

 during the last years of growth. 



Franz Boas. 



THE PROMISE AND POTENCY OF HIGH- 

 PRESSURE STEA3I. 



The writer has been so fortunate, recently 



as to be permitted to study the action of 



exceptionally high-pressure steam in the 



engine, under favorable conditions, and 



thus to add to the record of Jacob Perkins 



and his sons, and of Dr. Albans and others 



experimenting with steam of extraordinarily 



high-pressure, data which represents much 



more satisfactoi-ily the conditions now 



known by the engineer to be those essential 



to economic operation.* 



* The ' Promise and Potency ' of high-pressure 

 steam ; illustrated by the performance of the triple, 

 and the quadruple-expansion experimental engines of 

 Sibley College. Trans. Am. Soo. M. E., December, 

 1896. Vol. XVIII: No. DCCXVIII. 



The progress made to date and during 

 the century now elapsed since the intro- 

 duction by James Watt of the modern type 

 of steam-engine, as adapted to the per- 

 formance of every variety of work, has 

 been mainly through the steady advances 

 effected in the successful management and 

 application of steam of increasing pressure, 

 with corresponding thermodynamic gain by 

 increasing the ratio of expansion, and with 

 reduction of wastes, mainly by increasing 

 speeds of engine. The accessory gains have 

 been through expedients for improving the 

 lubrication, to reduce wastes of dynamic 

 energy, and for securing better protection 

 against external losses of thermal energy, 

 and improvements, as by jacketing and 

 superheating, resulting in suppression of the 

 internal condensation, due to the action of 

 the cylinder wall. 



Increasing steam pressure gives increased 

 mean effective pressures, and rising tem- 

 peratures of steam afford gains by wid- 

 ening the range of adiabatic and thermody- 

 namic transformation of energy. Super- 

 heating has not, as yet, been successfully 

 carried so far as to permit increased ther- 

 modynamic transformation by providing a 

 steam gas as the working fluid in the engine. 

 It practically simply insures dryer, and 

 thus better, working steam. Up to the 

 present time the risings, temperatures and 

 expansions have gone together, being limited 

 by the conditions which give us dry and 

 saturated steam. The result has been a 

 steady advance for a century, both in the 

 ' duty ' of the machine and its comple- 

 mentary elements, thermodynamic and me- 

 chanical efficiency. Watt insisted on re- 

 stricting steam pressure to seven pounds 

 per square inch on the score of safety ; we 

 now employ from twenty to thirty times that 

 pressure with probably no greater risk. The 

 work described in the communication here 

 abstracted was done at 300 to 500 pounds 

 pressure, and the boiler employed had been 



