Proceedings of the Polytechnic Association. 895 



of course, varied with different forms and sizes of springs; a flat 

 spring of equal section givinp; tlie least, about twenty-five foot- 

 pounds wlieu strained to its extreme elasticity, and a small clock 

 spring gave some 125 foot-pounds under similar circumstances. From 

 a large number of experiments I came to the conclusion that for the 

 style and size of spring which wouhl be required for sucli work, 

 forty -five foot-pounds was all that could be safely depended upon 

 in actual use, 



Now, as at least twenty per cent of the power of the spring would 

 be used up in friction of the machinery required to transmit its 

 power, it would take a spring capable of exerting not less than 090 

 foot-pounds to- drive a sewing machine one minute; and this would 

 require fifteen pounds of steel, or 900 pounds of spring, to drive a 

 sewing machine for one hour; and 9,000 pounds for ten hours! 



Again, the power of a strong nuin turning a crank is but 3,000 

 foot-pounds when working eiglit hours per day, but for a short time 

 he can exert about twice that power, or 6,000 foot-pounds. It would, 

 therefore, take him one hour and ten minutes to wind up a spring 

 which Vv'ould drive a sewing machine for ten hours. From th.cse fig- 

 ures it is evident that no form of spring power is applicable to this 

 pui'^^ose ; and it is still a problem for inventors to furnish some sim- 

 ple and cheap motor for this and similar purposes where a small 

 power onl}^ is reipiired. 



The Chairman remarked that according to the experiments of Mr, 

 Babcock, it would require but seven minutes, to wind up a spring 

 which would drive a sewing machine one hour; there are many 

 cases, wdiere this expenditure of povrer for seven minutes would 

 gladly be made, to secure the operation of the machine for an hour. 



However, he feared the statement of Mr. Babcock was too favor- 

 able. If a power is to be stored up for running sewing machines, 

 the elevation of weights will be found most efficient. 



Prof, J, A. IVhitney remarked, that the running of the sewing 

 machine has occupied the attention of inventors more than any 

 other. It seems that few of them take into consideration that the 

 m.ore force that is used, the more weight is recpiired. If fifteen 

 pounds of spring is required to run a nuichinc a minut(\ it would 

 tidce 900 pounds of spring to run it an hour. 



Dr. Vanderweyde stated that he had seen in rhiladoljthia a one 

 horse steam engine run some thirty sewing machines, and the only 

 objection the proprietor had to it was the cost of employing an 

 eno-ineer. 



