SCIENCE- GOSSIP. 



377 



CONDUCTED BY B. FOULKES-WINKS, M.R.P.S. 



EXPOSURE TABLE FOR MAY. 



The figures in the following table are worked out for plates of 

 about 100 Hurter & Driffield. For plates of lower speed number 

 give more exposure in proportion. Thus plates of 50 H. & D. 

 would require just double the exposure. In the same way, 

 plates of a higher speed number will require proportionately 

 less exposure. 



Time, 8 A.M. to 4 p.m. 



Between 7 and 8 a.m. and 4 and 5 p.m. double 



the required exposure. Between 6 and 7 A.M. and 



5 and 6 P.M. multiply by 4. 



Subject 



F.5-6 



F. 8 F.U 



F.16 



.22 



F.32 



F.45 

 ft 



F.64 



Sea and Sky . . 



Too 



TTu 



T5o 



j_ 



"3"2 



1 



Open Landscape 1 T _ 

 and Shipping 1 J iao 



_1_ 



32 



tV 



i 



i 



J 



1 



Landscape,with \ 

 dark fore- 

 ground, Street J-Jj 

 Scenes, and i 

 Groups . . J 



JL 



4 



1 



| 



1 



2 



4 



Portraits in | „ 

 Rooms .. ) 



4 



8 



16 



32 



- 



- 



- 



Light Interiors 4 



8 



1G 



32 



1 



2 



4 



8 



Dark Interiors 16 32 



1 



2 



4 



8 



16 



30 



The small figures represent seconds, large figures minutes. 

 The exposures are calculated for sunshine. If the weather is 

 cloudy, increase the exposure by half as much again ; if gloomy, 

 double the exposure. 



Cloud Negatives. — Owing to the sky in land- 

 scape pictures receiving, as a rule, some eight or 

 ten times the normal exposure, it is seldom that 

 we get any cloud effects in landscape negatives ; 

 it therefore follows that we must look to some 

 artificial means of inserting clouds in the picture. 

 The course generally adopted is to print clouds 

 into the picture by means of a cloud negative, 

 which may either be purchased ready-made, or the 

 photographer may prefer to make his own. We 

 adopt this latter method, and would recommend 

 the amateur to take every opportunity of securing 

 cloud negatives on the same size plates that he 

 generally uses for landscapes. These should be 

 indexed and full data attached, so that one can be 

 selected to suit any picture into which he may wish 

 to print clouds. We would lay great stress upon 

 this power of selection, as there is nothing so 

 objectionable in a picture as to see, perhaps, heavy 

 storm clouds printed into a picture of a bright 

 sunlight landscape. A very common error with 

 amateur photographers is to purchase one or two 

 cloud negatives, and to print these into every 

 picture they take. We need hardly point out 

 the absurdity of this practice. Another method, 

 and we think the most satisfactory, is to use 

 an isochromatic screen in conjunction with an 



isochromatic plate, and if to this can be added 

 a foreground shutter, fitted on the lens, the 

 best possible relation of densities can be obtained, 

 the different colours in the landscape are more 

 correctly rendered, and the most pleasing amount 

 of cloud effect will be secured. The intensity of 

 the isochromatic screen we prefer is one that re- 

 quires about three times the normal exposure, and 

 we may say that we have found the B. J. Edwards 

 Isochromatic Instantaneous Anti-Halo plates the 

 most suitable for all-round purposes. If these 

 plates are used, great care should be exercised 

 • luring development, as they are sensitive to the 

 yellow rays, and slightly so to the red. it is there- 

 fore necessary that all manipulations should be 

 carried out in a deep ruby light, and we advise 

 that the plate should be covered up as much as 

 possible during development, only uncovering it 

 occasionally to examine its progress. Where a 

 more pronounced cloud effect is desired than will 

 be obtained under the above conditions we recom- 

 mend that the sky in the negative should be locally 

 treated with a five per cent, solution of bromide of 

 potassium. This is most conveniently applied by 

 means of a small camel's-hair brush. Select one for 

 this purpose that is made in a quill and wound 

 with string ; do not on any account use a metal 

 one. The clouds in a negative may sometimes 

 be improved by a little judicious local reduction. 

 For this purpose we advise a weak solution of per- 

 sulphate of ammonium, which may be applied by 

 means of a tuft of cotton-wool. There is another 

 method of securing the true relation of clouds in 

 landscape negatives that has distinct advantages 

 over any other process where it is necessary to 

 make very rapid exposures, and the isochromatic 

 screen in consequence cannot be used. This 

 method consists of making two negatives of the 

 same view from the same position, one being 

 exposed for the landscape and one for the clouds, 

 the probable relation of exposure being one to 

 eight — viz. the cloud negative will require about 

 one-eighth the exposure required for the landscape 

 negative. These negatives are developed in the 

 usual way, and the print is then made from the 

 landscape negative. As a rule, the sky in the land- 

 scape negative will be sufficiently dense to give a 

 perfectly white sky on which the clouds in the 

 cloud negative can then be printed. If the sky in 

 the landscape negative should print through, so as 1 1 1 

 discolour the sky portion of the picture, it is 

 advisable to paint out the sky with some opaque 

 colour. This is best applied to the back or glass 

 side of negative, which will then give a landscape 

 picture with a pure white sky. The print is then 

 adjusted over the cloud negative in precisely the 

 same position, and the clouds allowed to print in. 

 care being taken to shield the landscape portion of 

 the print from the action of light by means of a 

 card, or brown paper mask, cut to the shape of the 

 horizon in the landscape. 



Thornton-Pickahd Catalogue.— We have jusl 



received a copy <>f the new Catalogue of the 

 Thomton-Pickard Manufacturing Company. We 

 notice this firm is placing oh the market a "new 

 patent iris shutter " which will work between the 



lenses. This should prove of great value to hand- 

 camera makers, and amateurs generally. There is 

 no doubt it can be relied upon as efficient, since all 

 goods of this manufacture by this firm are of the 

 most perfect workmanship and finish. The"Ruby" 

 ■ and '• Amber " cameras still hold a front place. 



