EARTH'S STUDIES ON BELTING 39 



for every condition of the surfaces of the belt and pulley- 

 no empirical formula could do this yet it does give values 

 which are perhaps very close to the true ones, when the belts 

 are maintained in accordance with the practice recommended 

 by Taylor which is outlined in Chapter II, and they agree 

 with the results obtained in practice. 



Working Tensions. The basic rule of practice adopted 

 by Mr. Earth is as follows: For the driving belt of a machine, 

 the initial tension must be such that when the belt is doing 

 the maximum amount of work intended, the sum of the ten- 

 sion on the tight side of the belt and one-half the tension on 

 the slack side will equal 240 Ib. per square inch of cross-sec- 

 tion for belt speeds; and for a belt driving a countershaft 

 or one in any other inaccessible location, this sum will equal 

 1 60 Ib. The maximum initial tension, that is, the tension 

 under which the belt is put upon the pulley when it is placed 

 in service and the tension to which it is to be retightened as 

 often as it falls to the minimum, must be such that the 

 above derived sum is 320 Ib. for machine belts and 240 Ib. 

 for countershaft belts. These values represent the constant 

 A in the mathematical discussion which follows and upon 

 which are based the horsepower tables on pages 91 to 94. 



With the above facts in mind, we can now examine the 

 formulae upon which the tables of horsepower and tension 

 are based. The complete mathematical discussion of their 

 development is contained in Mr.vBarth's paper, " The Trans- 

 mission of Power by Leather Belting," heretofore referred to, 

 and is there available for those who wish to follow it. Only 

 the briefest possible explanation will be given here. 



NOTATION 



h = tension in the tight strand of the running belt, pounds 



per square inch. 

 h = tension in the slack strand of the running belt, pounds 



per square inch. 



