212 



SCIENCE. 



[N. S. Vol. XVH. No. 423. 



the change from tension to compression, 

 which corresponds with a reversal of the 

 signs of the forces producing the stress. A 

 plus stress being tension, a minus stress is 

 compression, with no change in the line of 

 action. 



(c) A stress may or may not be consid- 

 ered per unit of area. There is nothing in 

 a stress to make it different from a force 

 in that respect. All forces are actually dis- 

 tributed forces, and all stresses distributed 

 stresses. A stress must be defined as to 

 its inherent nature, and not as to a method 

 of measuring it. Sometimes 'total stress' 

 is required, and sometimes the 'intensity' 

 of the stress, or stress per unit of area, 

 just as we speak of weight or weight per 

 cubic or square foot. That is, we may 

 wish to speak of the tension in a beam or 

 the tension per square inch. 



An examination of authors shows the 

 justice of these three points, although I 

 am not aware that they have been dis- 

 tinctly and positively affirmed, and the 

 importance pointed out of making them 

 clear in defining the word stress. 



A Systematic Method of Calculating the 

 Dimensions of Dynamo-Electric Ma- 

 chines: Cakl Kinsley, University of 

 Chicago, Chicago, 111. 

 The dimensions are so arranged that a 

 set of three simultaneous equations give the 

 relations existing between the diameter of 

 the armature, its length and the number of 

 conductors in the winding. 



These equations are primarily made to 

 depend upon considerations which will de- 

 termine the satisfactory operation of the 

 dynamo. The first equation is made to de- 

 pend on the electromotive force desired. 

 The second equation considers the rise in 

 temperature allowable. The third equa- 

 tion determines the efficiency of the ma- 

 chine. 



The intermediate assumptions, such as 



the area covered by the pole piece, affect 

 the ultimate dimensions, but all unite in 

 giving the essential features desired, 

 namely, the electromotive force, rise of 

 temperature and efficiency. 



Exhibit of a New Mechanical and Metal- 

 lurgical Product: C. A. Waldo, Purdue 

 University, Lafayette, Ind. 

 The new product was shown in two 

 forms. A thin spherical shell two and 

 one half inches in diameter, with a hole 

 one eighth inch in diameter through it, 

 and a reprodiietion in thin sheet copper 

 of a common quart whiskey bottle. Both 

 products had neither seam nor weld and 

 were not made by electro-deposition. This 

 is accomplished by a new process not yet 

 made public. 



Comparative Ductility of Steel under Grad- 

 ual and Impact Loading: W. K. Hatt, 

 "Washington, D. C. 



This note describes the results of tests to 

 determine the effect of rapidity of deform- 

 ation in tension on the ductility of steel. 

 Bars were tested: (1) Under a gradual 

 loading of about ten minutes' duration, 

 and (2) under one blow of a falling weight, 

 causing rupture in from .01 to .05 of a 

 second. The tests cover a range of steel 

 from soft steel castings and boiler steel 

 to hard tire steel. The material was all 

 of good quality. 



It is evident from the results that an 

 increased ductility may be expected under 

 impact conditions in the case of soft steel. 

 There seems to be a tendency under impact 

 to develop nodes of ductility in tension 

 bars, and sometimes two or even three dis- 

 tinct necks are formed. This may account 

 for the observed increase in ductility. The 

 phenomenon may be explained by the as- 

 sumption that the harder portions of the 

 bar transmit the shock quickly, throughout 

 the region that they occupy, to the softer 



