P^ffcJioio^irtiJ luVfMiijatfnJt 219 



increftsed in range he 1 m^tnitiunts. Thus \'' 



 ' struroent for l<^tiu^ uu* i>fn.>}>Ti.>'. ..f liitierenoes vi »i">-  

 «e described as a double weogv }':i t-nu'ter. one photometer beir._ 

 by the examiner and the other by the ex uniiitv. who endeavoars t 

 •' V - . - 1 -I examiner. Actual 1 \ CJalton got over the r a. 



~ » using shert- v>f >■> 'loured glass, each rot.i 

 on a horizontal wheel on the same axis, and which ci>uld thus be sec at 

 ' -other line of sight; a rotation of either wheel caused 



: <>in an . screen to pass through a greater thickness of 



the coloureil glass. Fot the measurement of white light Galton replaced 

 t he $:he«>ts of coloured glass bv gratuig& The whole apparatus was extremely 

 simple; the examinee, with his nead screened from tM light, kxJced throogn 

 a slit into a horizontal tube blackened inside, at the other end of which were 



' -^k on an illuminated screen. Inside the tube in 



~ w-ere placed the two wheels carrying the examiner's 



and the examinee's photometric sheets of glass diametrically, one was con- 

 trolled ' ' • . . • j.^j|j^ 



reoordt.. ^ ;.. — .- : - 'the 



goodness of the colour n. The great advantage of the in> 



over a wedge phot ' imy. but in the pov 



i:ives the exjierinic... ■^.•me disad\-antage a: - 



from the >-arying amount of 1 . ->cted from sheets at varying angle& 



Another instrume : the s ne*. but the details of 



which belong to an e. ^ vas s " f^^r "Determining R**- 



action-Time, This consisted of a fairlv Is pendulum. ^^ 



leased at an angle of 1 g its descent it 



_..v „ ,>^ •-""'! bv brushing ag.v..wc-^ « .^». ..g../^ .~.v. ^..-all mirror which 

 rt deoted ;. if or onto a screen, or on tbe other hand it gave a soond- 



sigTial liy a ii_ :'it being thrown off the pendulum by impact with a 



liollvw U'.\\ ^..v .^<>ition of the pendulum at either of these occ'-'-^"'^^ 

 is kr.own. The position of the pendulum, whoi the renmnse is mat. 

 sii::.a]. is ' by means c^a thread stretched narallel to the axis oi Ute 



pendulum elastic bands above and below and in a plane perpendicalar 



to that of . ion of the poMlalum. This thread moves fredy between 



two parallel bars in a horizontal plane, and pressing a key causes the bars 

 ' >^ "^p on the thread, just, iot illustration, as the bars of a paralM ruler 

 dose on the thread. This d^ermines the response-poation of the 

 iH'ntiulum, the moti<Mi of which is not suddenly checked by the clamping of 

 the thread, owing to the elastic bands. The horizontal bars are just bdow 



* I kaT« TCccnUj had aadi a pieoe of a^^pumtvs coaatr«c««d in tbe Biuttiic I^bontan 

 for tecnag penooal eqvataoo. Sbmb ■wrhinif 1 difieohf •row ia bringiag tbe t«o ookiaraa 

 vindows ade^patriy dose togoiha for rwnniMw iiiiiiiwi I aanMmntod tUs bjr «*d of a 

 pcJMi of Inmlfti apir, tho h iag f of tfco ortfaiy imy of oae ooaM bo jucti y o wd to the iw a gw of 



tke oxtoMrdiMiy ny of tfw oOmt, the other i—gew Imh^ eat off by a diaffcngHL Tte tU^ 

 tboroeri ' 



eofeaiiag of the border of Oe antr aord iaa iy nage was ieaad aq^igibleL ' Ihid. p. S&. 



* AabBilarpeBdahu^ad|iaa*BfafetoaB7til■eoroedIhAiol^iatheGall»Labo(a«olT,j«i* 



' - ^r 'rTj^rlinnHiiBMii \i\[\ flillii iia i lull 



»— 3 



