MACHINERY. 



thu5, that by accumulating a very moderate force exerted 

 during four or five turns of a fly, the wiiolc of it is exerted 

 on a punch, fet on a thick plate of iron, fuch as is em- 

 ployed for the boilers of tfeam engines, and the plate is 

 pierced as if it w?re a piece of chtefc. This accumulating 

 power of a fly has occafioned many, who think thcmlclvcs 

 engineers, to imagine, that a fir really adds power or mecha- 

 nical force to an engine ; and, net underftanding on what 

 its efficacy depends, they oi ten place the fly in a fuuation 

 where it only added a ufelefs burden to the machine. If 

 intended for a mere regulator, it fliould be rear tlie firll 

 mover : if it is intended to accumulate forcK in the working 

 point, it (hould not be far feparated from it.- In a ccrtain- 

 I'enfe, a fly may be faid to add power to a machine, be- 

 caufe by accumulating into the exertion of oue moment 

 the exertions of many, we can fometimes overcome an ob- 

 llacle that we nevirr could have balanced by the fame ma» 

 chine unaided by the fly. See I'Yy-wueel. 



It is this accumulaiion of force which gives fuch an ap- 

 pearance of power to fome of our firll: movers. When a 

 man i"; unfortunately catched by the teeth of a paltry coun- 

 try mill; he if crufhed almoil to mummy. The power of 

 ■%he llreaia is conceived to be prodigious, and yet we are 



certain, \ipou examination, that it amounts to the prefTure 

 of no more than fifty or fixty pounds ; but this force has 

 been atliiig for foTC time, and there is a mill (lone of a ton 

 weight whirling twice round in a fecond. This is the force 

 that crufiied the unfortunate man ; and it required it all to 

 do it, for the mill Hopped. We have been informed of a 

 mill in the neighbourhood of Elbingroda, in Hanover, 

 where there was a contrivance which difengaged the mill- 

 ftone when any thing got entangled in the teeth of the wheels. 

 On being tried witli a head of cabbage, it crnlhed it, but not 

 violently, and would, by no means, have broken a man's 

 arm. 



It is hardly neceffary to recommend fimplicity in the con- 

 ftru£\ion of machines. This feems now lufficicntly under- 

 ftood. Multiplicity of motions and communications increafe 

 friftion ; augment the unavoidable lofies by bending and 

 yielding in every part ; expofe all the imperfections of 

 workmanthip ; and have a great chance of being indiflintlly 

 conceived; and are therefore conlirut^ions wiihout fcience. 

 We fnall confider this objeft as applied to large machinery 

 under MiLL IVori. 



M.\cHiXEiiY /or manufaPurlng Cotton: See M.v*VFAC- 

 TURE of Cotton. 



IND OF VOL. XXL 





