waterman's dynamometek. 103 



one of which shows, by a slowly revolving index, the ex- 

 act distance which the horses haA^e traveled, without 

 looking at in for a distance of more than five miles. 

 The other dial ]Aate gives a perfectly accurate record of 

 the whole force expended from the commencement of the 

 experiment to its termination. In other words, it takes 

 all the difierent and varying forces, and adds them accu- 

 rately in one aggregate or whole, seen at a glance on the 

 dial plate under the eye. 



We shall attempt a brief description of the modes by 

 which the indexes on these two dial plates are moved. 



The mode by which the distance traveled is recorded 

 will be easily understood. A wheel one yard in circum- 

 Fi- 113 ^^^'^^^^ I'^ns on the ground and communicates its 

 motion by a cord, to a wheel attached to the dyna- 

 mometer. Tills, by means of an endless screw 

 and cog-w^ork, moves the index slowly around the 

 face, and thus records the distance traveled. There 

 are two parts of this portion of the apparatus, which 

 deserve a description. One is the w^heel around 

 which the cord passes in connection with the wheel 

 which runs on the ground. It is very important that 

 the exact number of the revolutions of tliis wheel should be 

 maintained, as compared with those of the ground wheel. 

 This is regulated as follows : The groove in this wheel is 

 made by screwing together two beveled edged wheels, as 

 shown in the annexed section, fig. 113. By placing thin pa- 

 per between these two wheels, the width of the groove 

 may be varied Avith the utmost accuracy, and the cord 

 consequently let further in towards the centre. The other 

 part Avhich Ave desire to notice, although not original in 

 this dynamometer, is the manner in Avhich the index is car- 

 ried around the face of the dial plate. There are two 

 cog-wheels on the same axis, one Avith a hundred cogs, 

 and the other with ninety-nine both fitting into the same 

 pinion. Consequently, Avhen one has made the entire rev- 



