540 ON DRAUGHT. 



In comparing animal liorse-power with that of the steam-engine, we 

 estimated it at about 125 lbs., but we believe that, with tolerably ^ood 

 horses, it may generally be taken at more than that. 



We have thus far confined our attention to the cases where velocity, as 

 well as duration of laboui-, was left to choice ; this is far from being always 

 the case. In stage-coaches, or other conveyances for passengers, speed is 

 absolutely necessary, and it only remains to learn how that speed can be 

 obtained with the greatest economy. The following Table, extracted from 

 Tredgold, will show the great reduction in the effect produced by increasino- 

 the velocity. ° 



The first column being the velocity or rate per hour, continued for six 

 Lours per day ; the second represents the force of traction of which the 

 animal is capable ; and the third the comparative effects produced. A 

 force of traction of 125 lbs. continued for six hours at the rate of three 

 miles per hour being taken as the standard, and considered equal to the 

 arbitrary number 1000. 



Miles per hour. Force of traction in lbs. Effect produced. 



2 166 888 



3 125 1000 

 H 104 972 



4 83 888 

 H 62i 750 



5 413 555 

 5| 36^ 500 



If, however, the hours of labour be lessened, taking the velocity correspond- 

 ing to the greatest useful effect, the results will be much greater, and the 

 velocity may be raised much higher, as will be seen in the followinsr 

 Table. ^ 



Here the first column is the length of day's work, the second the best 

 velocity corresponding to that time, or half the limit of velocity sho^vn in 

 Table (1), and the thu-d column the comparative effect produced, the forco 

 of traction being in each case 125 lbs. 



Duration of labour in hours. Velocity, miles per hour. Effect produced 



^ H 578 



3 H 709 



4 3| 813 



5 H 909 

 ^* 3 1000 

 7 2| 1063 



^ '^ 1110 



To attain higher velocity, it is necessary still further to reduce the load, 

 and the next Table is calculated upon the supposition of the strain bein^^ 

 only one-half the last, viz., 62^ lbs. ; this is about the average exertion of 

 each horse in a four-horse heavy stage-coach. 



Duration of labour, „ 



hours per day. Velocity. Effect produced. 



4 H 613 



3 6| 534 



2 , 7f 434 



1 11 307 



In mails or light coaches, where ten, eleven, and even eleven and a half 



or twelve miles an hour is attained, the average strain of each horse is 



barely 40 lbs., and the effect produced, or value of work done, not much 



more than one-half the above. 



It must be remembered, that these tables are aU calculated upon the 

 supposition of the road being good, and the work such as not to cause any 

 immediate injury to the animal, and is adapted only to the average quality 

 of horses. They are not, therefore, at once apphcable as data for calcula- 

 tions m all ordinary cases, but only serve to show the comparative forces 

 which may be exerted under different degrees of speed. The results or 



