XATLRL 



[October 3-, im c 



■i for reconsidering their policy is found by 

 the trustees in the Fact thai the very considerable 

 additions which have in recent years been made 

 to the ranks of the teachers promise to im]X)se a 

 strain on the funds of the foundation far beyond 

 their powers to support. 



rhi purpose of pensions is to ensure to the 



tea< her economic independence at the close of his 



lucttve life. Without such provision the work 

 of the teacher cannot be carried on without undue 

 care and apprehension, which lower the quality 

 of the teacher's work'. But then- is anothei point 

 to which attention is less often given namely, 

 the necessitv ol Freeing the teacher from the 

 apprehension of the economic dependence of wife 



and Family in the evenl of bis death. In tin , ,,s,- 



of the young married teacher this apprehension 



is probabl) more powerful and more detrimental 

 to good work than the former. A= the present 

 repent emphasises, however, the problem o< the 

 annuity cannot be financially separated from t he- 

 problem of life insurance during the productive 

 period of the teacher's life. 



I; is of much interest to notice that the eon- 

 i lusions reached here are fundamentally quite 

 similar to those arrived at by the commission on 

 the superannuation system for the federated 

 universities of ("ireat Britain. Whereas, however, 

 in Great Britain, owing to the comparatively small 

 number of teachers involved, and for other 

 reasons, the insurance and annuity contracts are 

 carried out through the agenc) of existing insur- 

 ance companies, the trustees of the Carnegie 

 Foundation have decided to found a special 

 teachers' insurance and annuity association to 

 be Organised, under the laws of the Stale ol New 

 York, so as to represent primarily the interests of 

 the policyholders, to whose scrutiny and over- 

 sight it would be subject. In ibis way insurance 

 can be effected at a lower rate than is possible 

 with insurance businesses carried on for profit, 

 and the benefits to be derived under the proposed 

 scheme appear to be appreciably greater than 

 those accruing under the British scheme. With 

 regard to the combination of life insurance with 

 annuity provision, the trustees point out that this 

 can be effected best by a combination of so-called 

 term insurance with deferred annuity insurance. 

 By tin- means, by the payment of the same total 

 sum is contributed under the pension scheme 



a mu. h i ater protection is given to the depen- 

 dents of the insured during his productive life, 

 without greatly diminishing the value of the 

 annuity should the insured live to the pensionable 

 age. Ill' suj ■ tion is well worth the considera- 

 tion of authorities in this country. 



ON COLOUR SJ . Si I 1SED PLATES. 

 JNDER the above titl< . in : issues of Nature 

 ^ of February [8 and 25, 915, we described 

 the general character ami sorw typical uses 



Olour sensitised plates that i plates made 

 sensitive to colours to which tin - mple gelatitlO- 

 ide of stiver is praeticall) insensitive. The 

 NO. 2553, VOL. IOJ ] 



additional sensitiveness is produced by the incor- 

 poration ol dyes with the emulsion or by their 

 application to the finished plates, and we pointed 

 out that when a continuous spectrum was photo- 

 graphed on sui li plates, there was 1 learly shown 



the original maximum of sensitiveness "! the 



siber bromide id the new maximum or maxima 

 added as the result ol the special treatment. 



Plates made sensitive to all the Colours ■■ 

 visible spectrum would thus have three or four 

 maxima, instead of only one. This irregularity 



was obviousl) "lie c.uise ol the difficult) i >l g 

 the complete control ol thl Colour effect il;.. 

 desn able. 



Shortly after those articles wen written, the 

 "Wratten Division" ol Messrs. Kodak imp.; 

 their panchromatic plate so effectually that it 

 showed an almost even sensitiveness to the normal 



solar spectrum. Messrs. Illord make ,1 plate with 

 similar characteristics. In these plates there is 



slight evidence of maxima in the greenish-blue 



and in the red, but these are so slight that il is 



often si.ineb necessary to take notice of them. 



It is obvious that a plate of even sensitiveness 

 is theoretically, and one may add practically, tin 

 best and simplest where the general .md various 

 control of colour elicits is necessary, for three- 

 colour reproduction purposes, lor example, where 

 the spectrum has to be divided into three regions 



roughly, red, green, and blue the expos,:-. 

 each colour is very nearly equal. For orthochro- 

 matic work that is, when- it is desired thai the 

 degrees of whiteness in the print shall correspond 

 in proportion with the degrees of luminosity in 

 the object that produces them, irrespective of their 

 colour -il is clear that we must use a colour 

 filter that will gradually tone down the action of 

 lln red and the blue, giving a curve of trans- 

 mission similar to the Luminosity curve of the 

 spectrum and such a filter will be green. The 

 general idea that a yellow filter is the proper one 

 to improve the rendering - of colour sensi 

 plates, which was correct with the older plales 

 that were deficient in red sensitiveness, appears 

 still to predominate. A yellow litter with modern 

 panchromatic plates will darken the representation 

 of the blues, but will leave the reds, and colours 

 sin h as yellow, of which red is a component, too 

 light. The difficulty is to find a suitable green 

 filter, for it is, as a rule, much more trouble to 

 get a green filter to suit fine's needs than that ol 

 almost any other colour. Of the well-known 

 dves, naphthol green seems the nearest approach 



to what is wanted, so far as absorption is con- 

 cerned. As Prof. Pope has been so successful 

 in his work on dyes, perhaps he will be able to 

 find one that gives a better curve and that air- 

 less ol tin colour that il is desired should be 



transmitted. < )f course, theoretically, for ortho- 

 chromatic results there is the alternative of re- 

 ducing- the sensitiveness of the plate to red to a 

 proper degree, leaving only tin action in the blue 

 ixiissive, and to be reduced by a yellow filter. 



We have jusl received from Missis. Ilford a 

 portfolio containing a set of comparative, prints 



