MR. GREGORY OtJ HOUSE rOWE-RS. 149 



s 



in whofe circumference the animal moves, the iL^fs fatigue will 



be occafioned by that kind of motion. Indeed" it is obvious, 



that lince a retflilinear motioivis the moft eafy -and natural ibr 



the horfe, the lefs the line in which he moves ife curved, v^'ith 



the greater facility he will walk over if, and the left he neeS 



recline from the vertical pofiliOn. Befides thi*;, with equal 



velocity at the circumference,' the centrifugal force will be 



lefs in the greater circle', ' wHlcfi will proportionally ditlii'ni'fti 



tiie fri6lion of the cylindrical palt of the trunnions, and the 



labour of moving the machine. And farther, the gi-eater the 



radius of the horfe-walk, the nearer the chord of the circle in 



which the horfe draws is to coincidence with the tangent, 



which is the moft advantageous pofition of the line of tradion. 



Hence it follows, that although a horfe may draw in a walk The larger 



of 18 feet diameter, yet he will work with far greater eafe in '^f^\^''^ ^°^ 



* -^ . ° . advantageous. 



One whofe diameter is 35 or 40 feet ; and rt is very defineable 



that an experimental enquiry Ihould be made to afcertain the 



proportion and abfolute quantity of work in drtferent circles, 



I am of opinion that it would not be difficult to make fonle Defcriptlon of a 



ufeful experiments, while work was adtually carrying on at "mechanical ap- 



any horfe mill, or machine where horfes are conftrained to meafuring the 



move in a circular walk. The fimple drawing which accom- re-a<^ion in mills. 



panics this letter will affift in conveying a clear idea of the 



method which -I fancy might be advantageoufly adopted; 



Let AB Fig. 1. Plate X. he the vertical fhaft to which the 



horizontal horfe poles AC, AD, are attached. Let one horfe 



work the madhine ^drawing at the ear E; but, inftead of 



the tranfverfe bar to which the harnef| is fixed being fimply 



hung upon the hook h, let a good fpriiJg fteelyard be inter* 



pofed between that crofs-bar and the hook, the graduations 



of which (liall, when the machinery is put into motion, ini- 



dicate the refinance (in lbs.) overcome by the animal, in» 



eluding the weight of the mafs moved, the fri<5lIon, &c. Near 



the extremity of the oppofite horfe-pole AD, let there be fixed 



a firong and correal comnaon fteelyard> whofe divifiofts (hall 



fliew the various weights from 40 or *>#lo 200lbs. and whofe 



centre of motion (ball be at the point/ on the fixed (land. 



Let the cord c which is faflened to the fliorter arm of this 



fleelyard, pafs (with as little fri6lion as poffible} over the 



pulley p, and thus, beinglurned into lh6 horizontal dire<5liott, 



or rather, inclining a little upwards, let it be fixed to the crofs 



. * bar 



