4,16 THE HUMAN MOTOR 



Continuous work for 3 minutes causes a certain fatigue. At 

 first this is confined to the right brachial triceps, the forearm, 

 and particularly the elbow joint. Next, the fingers of the right 

 hand are affected. Little fatigue is felt in the left arm. After a 

 long period of work the fatigue is less localised, and generally 

 affects, more or less, the whole of the upper portion of the body. 



314. Various Conditions affecting the Use of the File. The writer 



made a lengthy series of experiments with the object of determin- 

 ing the factors which influence, favourably or unfavourably, the 

 economical use of the file. Apart from the internal factors, ali- 

 mentation, health, physique, and so forth, there are the even more 

 important " external factors/' such as the position of the feet, 

 the general attitude of the body, the manner in which the tool 

 is held and manipulated, and the speed of the various motions. 



The table on pages 430 and 431 embodies most of the experi- 

 mental results obtained by the writer. 



The following deductions may be drawn from the foregoing 

 table : 



(a) Influence of Frequency. Up to a frequency of 80 strokes 

 per minute, an increase in the frequency of the strokes causes 

 a corresponding increase in the work done as measured by tke 

 weight of filings removed. Such a frequency is about the highest 

 at which the file can be satisfactorily used, and, above this figure, 

 the work done actually diminishes. It is very difficult to work 

 properly at 85 strokes, and almost impossible at 90 strokes per 

 minute, even for two minutes continuously. 



Working slowly, at 33 and 35 strokes per minute the hourly 

 production of work is 2,200 and 2,400 kilogrammetrts respec- 

 tively, the weight of filings removed being 20 grammes and 26-5 

 grammes respectively. At double these speeds, i.e., 66 and 70 

 strokes per minute, the production is more than trebled, i.e., 

 7,000 and 8,000 kilogrammetres, and 68 and 81 grammes of metal 

 removed, respectively. 



An examination of the experiments Nos. 1 to 39 in the table 

 show that a frequency of 79 strokes per minute gives the best 

 hourly production of work. It will be seen that, within the above- 

 mentioned limit, increase in the number of strokes per minute 

 causes more efficient utilisation of the muscular effort developed. 

 That of both arms together rises from 12 to nearly 18 kg., of 

 which nearly f is furnished by the left arm. It will also be seen 

 that the " useful effort " increases from approximately 4 to 8 

 kg., and, as this latter increases more rapidly than the total mus- 

 cular effort, the "co-efficient of utility" rises from 35% to 50%. 



(b) Influence o/ the Inclination of the Arms. In some cases 

 variations in the inclination of the arms, relatively to the plane 



