60 fjifr (till/ Liltri'H of Franris iialton 



This resolution led to Galton being pliiced on the Kew Committee, and 

 to an endeavour being made to raise the standard of angle-meiusuring instru- 

 ments in this country, and their comparison with those of foreign make. 

 The Royal Geographical Society was approacheil in the matter and that 

 Society passed a resolution to offer a prize of £50 or a gold medal to the 

 "Designer or maker of the most serviceable Reflecting Instrunient for the 

 Measurement of Angle* " — doubtless at the instance of its Honorary Secre- 

 tary. There exists a whole series of letters to Galton on the pomt. Sir 

 Edward Sabine in a letter of Feb. 1 (5 refers to both resolutions as Galton's. 

 The latter proposed a Kew certificate for sextants, and a study of errors 

 due to special forms of mercurial horizon, as well as of those peculiar to the 

 prismatic compass. 



{b) But Galton did not confine his attention to the above instruments. 

 In 1864 Casella brought out a pocket 'altazimuth,' "improved and modified 

 by the kind assistance of Francis Galton Esq. F.R.S." It could he u.sed in 

 two positions, in one as a good azimuth compass, and in another as a weighted 

 disc for altitudes. It could also be used as an ordinary compass or as an 

 ordinary clinometer'. 



(r) Galton also designed for Casella a small pocket instrument termed a 

 Zeonu'ter^ (from Greek {c'w, boil), Ijy means of which with an ounce of water 

 and drachm of spirit the height of any mountain could be obtained and 

 index correction of the aneroid determined ; Galton provided a table of cor- 

 rections for cases in which there was a considerable portion of the mercury in 

 the stem of the thermometer outside the vessel containing the boiling water, 

 and this table accompanied the directions for the use of the Zeometer. 



((/) There is the design of another instrument to show by the action of a 



{)iece of catgut or of whalebone strips on the motion of a clock the number of 

 lours per day in which humidity has exceeded a datum value. Galton con- 

 sidered that a similar arrangement could be made for temperature. 



(e) Details of a linkage for determining the conjugate foci of a lens 

 mechanically'. 



(/) A note on lighthouse signals. Galton notes that the period of a 

 complete breath is very nearly and very regularly four seconds. That this 

 four seconds as a period recognisable by everyone should be taken as the 

 base unit for lighthou.se flashing signals. 



(g) The original design of the hand-heliostat, with diagrams of its 

 working and a water colour illustration of the field of view witli the mock- 

 sun covering the requisite flash point of tlie landscape. See p. 11> above. 



(A) An instrument termed the "Tactor" machine. The diagram shows 

 it to consist of two levers each with a tooth working on one of two com- 

 plicated eccentrics on the same axis and apparently causing certain blocks 

 to rise, fall and grip. I have no idea for what purpose the "Tactor" machine 



' There exists still Qalton's determination by aid of it of the latitude of llutjnnd Uate! 



' Then; are very full detaiU for the construction of this instrument, apparently in the draft 

 of a lett<;r to Casella. 



* TtiiH occupied Galton af^ain later, when he wa.s busy with photographic change of scales, and 

 in conjunction with Mr (now Sir) Horace Darwin a very rea-sonable linkage was devised t<j keep 

 object and focal plane image at their proper distances from the optical centre of the objective. 



