776 VETEEINAEY HYGIENE 



Experiments have been made to determine the effort 

 required to move a load on London streets. A gross load of. 

 4 tons was drawn at a speed of from 2 to 6 miles an hour, 

 and the following were the mean results in traction force 

 required per ton : 



Lbs. Lbs. 



Macadamized surface ... ... 40-7 to 44-29 



Asphalt ... ... ... 39-0 to 39-32 



Wood pavement ... ... 33-62 to 36-63 



Granite sets ... ... ... 26-20 to 27-00 



These experiments were made on a level road ; when the 

 draught is uphill a portion of the weight of the carriage 

 must be added to the draught on the level. For example, 

 if the draught on the level for a carriage weighing 12 cwt. 

 amounted to 1^ cwt., and a hill rising one foot in four has 

 to be ascended, then J of the weight of the carriage must 

 be added to the draught on the level, viz., 3 cwt. must be 

 added to the original 1^ cwt. 



In the streets of Glasgow an average single horse load, 

 inclusive of the dray, is 8J tons ; in London a dray horse 

 is not required to pull more than 2|- tons ; but the horse in 

 the North does his work at a walk, whereas in London he 

 has to do it at a trot. 



We have referred previously to Watts' classical experi- 

 ment whereby he determined with brewers' horses what is 

 known in engineering as Horse Power. He found that a 

 horse was capable of pulling a weight of 150 lbs. to a height 

 of 220 feet every minute; this is equivalent to 33,000 lbs. 

 lifted one foot high every minute (150x220 = 83,000), and 

 this is adopted as the unit of work in all engines. 



There are many reasons which lead to eight hours being 

 selected as the length of the working day, and it has been 

 considered by those not conversant with the practical 

 management of horses, that a fair day's work for a horse is 

 33,000 lbs. (14-7 foot tons) lifted one foot high every 

 minute for eight hours ; but this is far too high for general 

 application, it amounts to 7,000 foot tons per diem, which 

 is a very hard day's work. Further, though at slow draught 



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