Tlicsr two oxninplcs niust not be taken ns itldicntitig tlurt tho stnntlnrd glnsscs, supplicd with the tintomoter, . nrc riot truo ns fnr ns tlicir prirnnry colour is concorncd, but siiiiply tlirrt their propert of stopping wliito ligliC Ims k c n ignoteil. ~h u s 0.1 of yc~%\v is 0.1 of y o ~~o w , but nlso a b u t 0.3 tf grey. Tlint the gliisscs nim correctly stnudardhd \VRS 8hown by hnvhig the 8u)tid tweiber o/ glaaaca in any two cornliinntions compnrcd, 80 ns to cnnccl out tho moyness. Tliu I ~~v i b o n t l Tintoinot.cr is being niorc nntl niorc uscd its n convenient instruuicnt for tho ii\ciisuronmit rncl recording of colours. Tho theory of tho tintonictcr is that any colour cnii bu inntolied with n suitriblo combinntion of red, yellow trntl bluo stnnderd glnsscs. 111 using the Iuvibond Tintonictm 1 found tlint it \vns possible to ninko ghtsacs of clilTcrcnt V J L ~R J l l ~l f X h thc tjnnio colour or match oiiu auotlior, for usaniplc : 3.0 Ited 5.0 Ycllow 1.0 Blue 2.2 Red 4.2 'I'cllow 0.2 13luc In o.sainining it body with this colour, ttvo cs~~criincnturs with Iwrfcct OycHight might correctly record dillcrcnt results. This is n i i obvious objection to tlic use of tltc itistruniolit, irntl tlrcrcforo 1 thought it worth while to find t.ho enuse, iii order. tlutt this Imssibility of obtriinirig incoiieistcnt msults might be eliiniiintcd. the stwdnrd glnsscn nro not porfcotly Lrnnapnrmt to wliitc light ; nnd hcnco n little wliitu liglit is lost for cncli glnss tlint is pnsscd tlirough. Tliis is dint oiiu \voultl nnturnlly cxpcct, for Iwrfectly triinxl)irrcnt bodies fire unknown, Imt 1 IULVO.IIOL sccn it niciitioncd nny\vlicre tlint tlic nniount Of liglit HO lost inust bo considered in rccortliiig tliu colour. r)f n largo number of coiii11nrii~on~ of conilJinntions of glosscs, tliu followin iirc sclcctctl to illustnttu Lliis p i n t . (1) (It w h be ruriioni~~urcd tluit tlia gtnndartl glusscs itrtj intandcd to be t10 erriiiigctl tlinf cquril ntiiouiits of rctl, jvllow tru.d blue givci it noutrirl tint. i\c~uiilly, HilCh coiniinationa do givu greys itlniost free from uolour.) A coni-Ihirtion of 12 glrrsscs : '2, '2, -2, '2 Red '2, '2, '2, * :! YCllO\. 2, -2, 2, .2 I3ltto iloos not giro the suuic -6: Rod -8 Blue IiuL gives tlio uinio gtuy (is tho tlircu glessus : 4.0 Itcd , 4.0 Ycllo\r 4.0 13lllO