.340 



SCIENCE. 



[N. S. Vol. XVI. No. 400. 



more) receiving telephones, so that one 

 (or more) observers could hear the combi- 

 nation or algebraic sum of the tones. Now 

 the tones being adjusted to equal strength 

 bj' the adjusting screws and to the opposite 

 phases by revolving one of the mounted 

 magnets, the receiving telephone gave no 

 sound, and this condition of things was evi- 

 dence that the teeth at both ends passed 

 before their magnets at the same time. Now 

 the zero having been determined with the 

 propeller disconnected, it remained only to 

 observe the angle through which the ob- 

 serving magnet had to be moved when the 

 shaft was running under torsion, to have a 

 measure of the twist of the shaft. 



The apparatus gave perfectly accurate 

 results with a precision of from one quarter 

 to one per cent. The zero was readily and 

 certainly obtained by a particular method 

 of observation and in spite of the noises of 

 the running machinery, and the results re- 

 quired only a single multiplication to give 

 the horse-power corresponding to any par- 

 ticular observation. A model of the 

 dynamophone was exhibited to the Section, 

 with photographs connected with a recent 

 test of the new turbine yacht Revolution. 



The Deflection of a Complete Quadrilateral: 



J. BuEKiTT Webb. 



The object of this paper is to outline a 

 method which I have used for some years 

 at Stevens Institute for investigating the 

 stresses in framed structures with super- 

 fluous members. Suppose we consider ac as 

 superfluous and imagine the joint a to be 

 constructed as indicated in the figure. 



Now remove the weight and screw up the 

 nut until the perfectly definite stresses thus 

 produced in the members amoimts to some 

 convenient amount, say a tension of minus 

 40 in cb. An ordinai'y force polygon is 

 then drawn, giving the corresponding 

 stresses in the members, and, the material 

 and dimensions being known, the strains 



due to these stresses are tabulated for all 

 the members. 



This primary part of the process is com- 

 pleted by finding the displacements of all 

 the joints and the lower end of a by means 



of a displacement polygon (treated of in 

 a paper before Section A), which gives the 

 distance Avhich the nut must be screwed up 

 to produce the assumed stresses. 



Secondly, the nut is run down entirely 

 out of the way and the weight put on to 

 produce a stress of plus 40 in be and 

 another force polj^gon is constructed with 

 its corresponding deflection polygon. 



The final operation is to screw up the nut 

 any desired distance and then add the 

 stresses thus produced to those already due 

 to the weight. Evidently the final stresses 

 consist of the weight stresses plus the 

 primary stresses multiplied by a fraction, 

 the denominator of which is the distance 

 determined as corresponding to the minus 

 40 in be, and the numerator of which is the 

 distance the nut may be finally screwed up. 



A New Photometer for the Measurement of 

 the Candle-power of Incandescent Lamps: 

 Professor C. P. Matthews, Purdue Uni- 

 versity. 

 Nearly everj' one in this age of electric 



