8 



C. Bar us — Spiral Goniometry in its 



This is the method to which the above simple designs are 

 tributary, and the diagram of an apparatus for measuring the 

 work put out by a shaft in a given time is given in figure 5, 

 in longitudinal section. 



Let ab be a long rod whose torsion coefficient is of known 

 suitable magnitude, and suppose the end a to be put in con- 

 nection with the shaft of the motor and the end b with a 

 tachometer or revolution counter, and let cc be the journals in 

 which this rod revolves. The rod is concentrically surrounded 

 throughout the greater part of its length by the stiff tube ee, 

 one end of which may be rigidly joined to the rod near a by 

 a set screw. The other end of the tube with the attached dial 

 del is capable of revolving around the rod in virtue of a 

 journal, unless resisted by the set screw in question. Suppos- 

 ing the latter fixed and the shaft revolving, twist may be im- 

 parted to the rod by means of the friction pulley p, and its 

 amount measured by the index nn fixed to the rod immediately 

 in front of the dial del, in the manner shown in the above 

 paragraphs. S is the stationary scale with numerals to facilitate 

 the reading, and it is attached to the base B together with the 

 journals c, c. When no friction is applied at p the rod ab and 

 tube ee spin around together in such a way that no angular 

 deviation between index nn and dial eld is registered. When 

 a suitable frictional resistance is applied, the index will be dis- 



? 



&<J 



r- 1=1 



-d 



* «///////&/7?/zff? 



bl 



r 







c 





---£• 





-d 





"Tl 





? 







placed in angle relative to the dial, by an amount proportional 

 to the frictional resistance. The efficient part of the torsion 

 rod is clearly the length within the tube, and if by a prelimi- 

 nary calibration the intensity of the torsion couple per degree 



