632 



Life and Letters of Francis Gallon 



apparatus of this kind, and several arrangements for doing so are described 



(P- 251 )- 



Galton further gives an account of various modifications of his instrument 



which he had made with revolving discs and multiple lenses. Also he 



explains how " to present the images formed by two successive glimpses as 



simultaneous pictures seen side by side in the field of view." 



Finally we may note how Galton measured the velocity of his instrument. 

 He put in temporarily a peg which checked the velocity of the recoil when 

 the slit was opposite the eye-hole. Then the stud being held down, and the 

 box fastened tightly to a support, the recoil was used to project a light weight 

 into the air ; this it did when the lever came against the temporary peg, and 

 the weight was projected three inches : The velocity of the stud was therefore 

 j2gS/\2 ft. per sec. = 4 ft. per sec. = 48 inches per second. From this the 

 velocity of the slit could be easily found by the known distances of stud 

 and slit from the centre of the pin C (p. 250). Assuming that measurements 

 can be safely taken on Galton's figure, I make the distances of stud and slot 

 from centre of pin to be in the ratio of about 35 to 56 or 5 to 8 or the 

 velocity would be 384/5 inches per second, and length of exposure g^jth of 

 a second. Galton gives it in his actual instrument as 3<hyth of a second. 



I know no reference by Galton to this paper in his later publications, nor 

 am I aware of any work on Galton's lines done since its appearance. 



Addendum II 



"Note on Australian Marriage Systems." This paper appeared in the 

 Journal of the Anthropological Institute, Vol. xvin, pp. 70-72, 1888 

 (published 1889). Galton gives a simple explanation of the well-known 

 Australian Kamilaroi marriage system, which we can condense as follows: 



Galton illustrates this as follows: Suppose there were only two Uni- 

 versities (Oxford and Cambridge) and two University clubs (the Oxford and 

 Cambridge and the Universities clubs), and assume them all open to men 

 and women alike. Then a man (or woman) may not marry a woman (or 

 a man) of the same university and the same club as himself (or herself). 

 The children of Kamilaroi will be entered at the Mother's university 

 (P or Q) and the Father's club (1 or 2). In the case of the Kiabara the 

 children on the other hand would be entered at the Father's university 

 and the Mother's club. If this be not the theory of the arrangement, it is, 

 as Galton remarks, an easy way of remembering the complexities of the 

 Australian system. 



