42 ANNUAL OF SCIENTIFIC DISCOVEKT. 



It niisfht be worlli Avliile to try this for laying iJio Ijricks of our 

 chimiu'y.s, which are so rapidly destroyed and rendered daniijerous 

 by the gases from burning anthracite. — Journal of the Fmaldin 

 Institute, July, 18G6. 



S. r. EUGGLES'S DYXAMOMETER. 



At the meeting of the American Acadeni}' of Arts and Sciences, 

 held January 9, 18<)G, Prof. Charles W. Eliot exhibited and 

 deseril)ed a \w\y kind of dynamometer, invented by Mr. S. P. 

 lluggles of Boston : 



'* This new and admirable invention accomplishes two objects; 

 first, it measures the exact amount of power whieii is being 

 consumed in driving a single maeiiine, or any nunilter of ma- 

 chines, at any instant of time, indicating every change in the force 

 recjuired, as the work done by the machines varies from instant to 

 in^tant; secondly, the apparatus adds up and i-egisters the total 

 amount of power whicli has Ijeen used by any machine!, or set of 

 machines, lUning a da\', a week, a month, or any desii-ed time. 

 Tlu! apparatus may be thus desci'ibed. The pulley from which 

 the power is taken, is attaciied to tiie shaft by the intervention of 

 a sj)iral sjiring. One end of tiiis spring is secured to the sliaft, 

 and the otiier end to the hub of the pulley. The lateral motion 

 of the ])uliey upon the shaft is previ-nted by a colhir on cither 

 side of the ])ulley. On the inside of the huij is cut a screw of 

 al>out three-ineli jMteh, that is, a screw which makes a comjjlete 

 turn within a distance of about three inches measun^d on tiie axis 

 of the hub. A rectangular slot is cut out of tiiat part of the sliaft 

 which lies within the hul) of the pulley, and in this slot slijis back- 

 wards or fcn'wards a piece of metal whicli jn-ecisely tits the slot. 

 From each side of this small piece of metal, there i^rojects beyond 

 the surface of the shaft a small portion of the male screw which 

 exactly fits into the screw cut in the interior of the hul) of the 

 pulley. If there be no resistance at all to the motion of the pul- 

 ley, shaft, spring, and pulley will all start together, and I'cvolve 

 together. But if a resistance be offered to the motion of the 

 pulli'V, the shaft, and with it the piece of metal which slips in the 

 slot, will start first, and the pulley will move only when the strain 

 caused by the twisting of the spring is sufficient to overcome the 

 resistance a])plied to the circumference of the pulley. But if the 

 piece of metal in the slot begins to turn while the hub of the ])ul- 

 ley is stationary, the piece must move laterally within the slot, 

 being forced by the screw. If the pulley starts a quarter of a turn 

 later than the shaft, the piece will move laterally three-quarters 

 of an inch ; if the pulley st;irts a half a turn later than the shaft, 

 the piece Avill move laterally an inch and a half. The lateral 

 motion of the piece in the slot is proportional to the retai'dation 

 of the pulley, and this retardation is proportional to the strain 

 upon the belt which passes over the pulley, and convej-s the power 

 to be used. To the movable piece in the slot is connected a small 

 round rod, which runs out through the centre of the main shaft 

 and i^rojects some little distance beyond it. On the end of this 

 rod is a circular rack of teeth, in which plays a pinion, on whose 



