642 A MANUAL OF VETERINARY PHYSIOLOGY 



horse could raise a weight of 150 pounds passed over a pulley at a 

 rate of 220 feet a minute (equal to 2.\ miles an hour) : 150 x 220 = 

 33,000 pounds lifted 1 foot high per minute, or 33,000 foot-pounds 

 per minute. From that time, on the basis of Watt's original excessive 

 estimate, the most extravagant demands have been made on the 

 strength of horses, for which engineers and mathematicians, who 

 alone have studied the question, have been responsible. A horse 

 can, of course, raise 150 pounds at the velocity mentioned, but the 

 practical question is for how long ? He could do it for three and 

 a half hours and not be overworked, but eight actual working hours 

 are expected from him, and the standard then becomes excessive. 

 Horses ploughing frequently exercise a force of 150 pounds, but 

 here the pace is the saving factor. 



Mechanical daily work is the product of three quantities — the 

 effort, the rate, and the number of working hours. The difficulty lies 

 in determining the effort ; there is no means of ascertaining this with 

 any degree of precision in riding-horses, but with draught animals 

 the introduction of a dynamometer registers it with sufficient 

 accuracy. It is evident, however, that the force of traction varies 

 with the character of the roads, and in practice it is found that even 

 on a fairly level surface it varies from moment to moment, depending 

 upon the size of the obstruction or the nature of the irregularities 

 met with by the wheels. There are many other features, apart from 

 the nature of the road, which influence the question of effort in 

 draught — for instance, the height of the wheels, the width of the 

 tyre, the presence or absence of springs. Thes3 points are only 

 referred to ; they belong to the realm of mechanics, but their physio- 

 logical bearing in increasing or reducing the effort required is well 

 known. Experience goes to show that eight hours' work at a 

 walking pace of three miles per hour, with a load drawn without 

 difficulty though with effort, constitutes a working day. If the 

 load or pace be increased, the period of labour must be reduced. 



The amount of work performed is spoken of as foot-tons or kilo- 

 gr ammeters — viz., so many tons raised 1 foot or so many kilo- 

 grammes raised 1 meter. The published tables of work by 

 Redtenbacher, Rankine, Morin, etc., are all too high. These place 

 the normal daily work of a horse at from 6,200 to 6,700 foot -tons 

 (1,926,544 to 2,071,104 kilogrammeters) . Kellner and Wolff, in 

 their experiments on nutrition in horses caused 2,154,000 kilo- 

 grammeters of work (7,000 foot-tons) to be performed daily on a 

 circular dynamometer,* but the writer believes that the following 

 more closely approximates to what should be demanded for regular 

 daily work : 



A moderate day's work = 3,000 foot-tons. 

 A hard day's work =4,000 foot-tons. 

 A severe day's work = 5,000 foot-tons. 



As a means of conveying to the mind the value of quantities 

 which cannot be visualised, the work in the following table is 

 equivalent to 3,000 foot-tons, it being assumed that the weight of 

 the animal, in addition to the weight carried, is equal to 1,000 pounds : 



Walking at 3 miles per hour for 8*7 hours. 

 >> 4 >» >> 5*3 >> 



>> 5 »» »> 3/»» • 



Trotting 8 „ „ 1*5 „ 



Cantering 11 „ ,, ro „ 



* This is the amount Watt's horse would have performed in eight hours. 



