220 



Life and Letters of Francis Galton 



a horizontal scale which is 800 mm. below the point of suspension of the 

 pendulum. Galton provides a table for reading off the distances along the 

 scale from the vertic^d position of the pendulum in terms of the time the 

 pendulum takes from the vertical position to the }>osition in which the thread 

 IS clampe<l. The reaction time is thus ascertainable on the assumption that 

 the time from pressing the key to the mechanical clamping of the thread is 

 negligible ctiinpared with the reaction time. It would however be easy to 

 correct for this, if we armnged occasionally for the pendulum to work the 

 clamping key itself, and so ascertained the time of clamping independently 

 of the living l)eing's reaction and response. 



Another instrument designed by Galton was intended to measure the 

 rapidity of a blow, or indeed trie rate of movement of any limb'. The principle 

 of the mechanism is that the limb , _ 



is attiiched by a string to a light 

 mechanism which draws in the 

 string at a faster rate than the 

 limb moves. The motion of the 

 string is checked when the limb 

 reaches its full extension, but a 

 light weight on a jilatform con- 

 tinues to rise freely and measures 

 by the height it reaches the 

 velocity of the platform (and of 

 the string) when the string was 

 checked. The whole scheme is 

 indicated in the accompanying 

 diagram. .47^ is a stretched india- 

 rubberlwind; intheactual machine 

 as worked this was much longer 

 than indicated in the diagram. 

 liC is a thin steel wire to which t ' 



the conical platform D is firmly ^ vi^ 



attached, an ivory cylinder ii rests 

 on the platform and runs loosely 

 on the steel wire. When the 

 platform D is checked, E goes 

 forward with Us final velocity 

 and this velocity is measured on 

 the scale behind BC according 

 to the height to which E rises. 

 A string passes from the vertex 

 of C and is wound round and ultimately fastened to one wheel F of a 

 differential pulley. Another string is wound round the second wheel G of 

 the differential pulley and ultimately fastened to it ; the remainder of this 

 string is made horizontal by being carried over a small pulley. To the 



' Journal of the Anthropological InstituU, Vol. xx, pp. 200-204, 1890. "A new Inatru- 

 nient for McoHuring the liate of Movement of the various Limbs." 



30. 



20. 



10. 



'U 



w 



e 



