284 Life and Letters of Francix Galfnti 



Huperimpoution of the jiortraitB, such as I had frequently employed with maps and nieteoro- 

 logioal tnMses, that the idea of composite figures first occ-urre<i to me'." 



Thifi pvj)er by Galton, wliich I had some difficulty in locating, and of 

 whicli no copy could l)e found in his collections, is entitled : " On me^uis of 

 combining various Data in Maps and Diagrams'." Galton therein refers 

 again to his stereoscopic niaji method', which plan he regrets had not yet been 

 adopted. He says that it needs good models, but that the number of the^e 

 increases every year, as the then recent French Geograj)hical Exposition de- 

 monstrated. He exhibited in the Ix»an Exhibition stereoscojiic views of mmlels 

 taken by the Royal Enginet^rs, but I do not know what subjects they rei)re- 

 sented. He suggested tue stereoscope, not only as a means of showing thmgs 

 in the solid, but of superposing plans and maps for comparative purj)oses. 



He next turns to superposition by means of a telescope ; he remarks thai 

 if one half of the object-glass be covered up, the sole effect on the image of a 

 distant object will be to reduce its brilliancy by a half. Now let us suppose 

 two lenses placed one in front of one half of the object-glass and the other 

 in front of the other half, each with its own object at its focal distance ; the 

 two objects will then be combined superposed in the field of view of the 

 telescope. Instead of two lenses four might be distributed over the area of 

 the object-glass to combine four objects, etc. Actually Galton placed his 

 telescope vertically and ran a horizontal tramway under the objective; in the 

 blackened roof of a 'tramcar' a number of lenses were inserted and opposite 

 each on the floor of the carriage its own object at the focal distance of the 

 lens. If now lens 1 be brought under the objective we see only object 1 , 

 as we push the carriage farther lens 1 tends to pass out of the field and 

 lens 2 to share the field ; thus different intensities of objects 1 and 2 can 

 be combined. A further push of the carriage causes 2 alone to be seen, and 

 the process continued combines it with 3, and so on. Galton's model had six 

 lenses of the same focal distance and size in the roof of his carriage. By this 

 means a series of geographical data which would overcrowd any single map 

 can be combined in sets of two. 



" It affords a peculiarly suitable method for picturing changes whether in physical or 

 political geography. 1 will not describe the mechanism by which complex and powerful in- 

 struments of this kind might be constructed ; where the images should be thrown by a lime 

 light on a screen, and a string of perhaps only three large achromatic collimatore would serve 

 for an indefinite number of pictures." (p. 315.) 



That Galton should have spoken of the old ' wheel of life ' in connection 

 with his apparatus, shows that ne had a foreshadowing of the modern cinemato- 

 graph. By using lenses of different focal length objects at different distances 

 could be combined, and by using inclined mirrors facing definite parts of the 

 object-glass the objects need not be placed in parallel planes. 



• Journal of the Anthropological Iiulitnte, Vol. viii, p. 135, 1878. In this pap<!r (ftn. p. 136) 

 Oalton gives 1878, instead of 1876, for the year of the Map paper. 



' South Kensingt^Hi Museum Conferences held in connection with the Special Loan Col- 

 lection of Scientific Apixiratus, 187C ; Chemistry, Hiology, Physical Geography, Geology, 

 Mineralogy and Meteorology (pp. 312-15). London, Chapman and Hall. 



' See our p. 33. 



