42 Professor Gordon on Dynamometrkal Apparatus. 



instnimont, — 1st, Its sensibility should be proportioned to the intensity 

 of the efforts to bo measured, and ought not to alter by usage. 2d, 

 The indications of the efforts must be registered independent of the 

 attention, the will, or the preconceived notions of the observer, and, 

 consequently, should be furnished by the instrument itself, by means 

 of lines traced, or other results available at the conclusion of 

 the experiment. 3d, The effort exerted at each point of the space 

 passed through by the point of application of the power should be 

 ascertained, or, the effort at each instant of the duration of the observa- 

 tions. And 4th, If, from the nature of an experiment, it must be of 

 long continuance, the apparatus must admit of easily summing the 

 amount of mechanical effect expended. 



The beautiful idea suggested by Poncelet of integrating mechani- 

 cally the EFFORT as a function of the distance passed through^ was ex- 

 plained in Morin's compteur; and it was shown that M. Morin's Dyna- 

 mometrical apparatus completely fulfils all the conditions above laid 

 down. 



Full size drawings of the Dynamometers as made for experiments 

 on friction, — on the draught of wheel carriages and ploughs, — and on 

 that of canal boats at great velocities, — as also, for application to 

 measuring the mechanical effect expended in working machines, and 

 tools having a rotary motion, — were exhibited and explained. Com- 

 pared even with the friction brake of Prony, or its modification by 

 Navier, and with a most ingenious Dynamometer for rotary motion, 

 by Mr. Smith of Deanston, of which a model was exhibited, the ap- 

 paratus of Morin was shown to be a great advancement, — measuring 

 mechanical effect, or work done, with the same precision as bread is 

 weighed. 



The application of the apparatus, somewhat modified, to measuring 

 and registering the mechanical effect produced by a steam-engine at 

 its piston, was illustrated by drawings. This application, in the hands 

 of Professor Moseley, has undergone various modifications and im- 

 provements; but the Indicator'* (for the construction of which the 

 British Association granted £100,) has not yet been applied. When 

 completed, it will afford a means of ascertaining the duly of steam- 

 engines, infinitely more to be relied upon than those hitherto em- 

 ployed ; and its applicability to marine engines and locomotives, as 

 well as to fixed engines, greatly enhances its value. 



* Since this paper was read, I have seen Professor Moseley's Indicator applied. The 

 improvements and new adaptations of the principle of Poncelet are admirable. A 

 detailed description and theory of the new Indicator are given in the Reports of the 

 British Association. — L. G. 



