2 So 



SCIENCE- GOSSIP. 



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



EXPOSURE TABLE FOR FEBRUARY. 



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

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

 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, 11 a.m. to 1 p.m. 



Between 9 and 11 a.m. and 1 and 3 p.m. double 



the required exposure. Between 8 and 9 a.m. and 



3 and 4 p.m. multiply by 4. 



Subject F. 5-6 



F.8 



F.ll 



F. 16 



F.22 

 i 



F. 32 



l 



F.45 



F. 64 



Sea and Sky . . 



iio 



55 



32 



Te 



1 



Open Landscape 

 and Shipping 



}* 



t\ 



£ 



1 



4. 



I 



1 



2 



4 



Landscape, with 

 dark fore- 

 ground, Street 

 Scenes, and 

 Groups 



Y 



i 



i 



1 



1 



2 



4 



8 



Portraits in 

 Booms 



\« 



16 



32 



1 



2 



4 



- 



- 



Light Interiors 



30 



1 



2 



4 



8 



16 



32 



60 



Dark Interiors 



2 



4 



8 



16 



32 



60 



120 



240 



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. 



Photographic Year-Books. — "VVe have received 

 several photographic year-books, some of which 

 are beautifully illustrated. These will be noticed 

 at greater length in an early number. 



Photographic and Optical Trades Exhi- 

 bition. — This exhibition, which promises to become 

 an annual event, will be held as heretofore at the 

 Portman Rooms, Baker Street, - London, from the 

 11th to 19th of April, 1902. In looking through 

 the prospectus and plan, we see that in addition to 

 the photographic trade it is proposed to incor- 

 porate exhibits from the optical trade. This, we 

 have no doubt, will make a more interesting and 

 complete exhibition than previously. We con- 

 gratulate Mr. Arthur C. Brookes, the promoter, 

 and wish him good fortune in this case. If this 

 exhibition proves the success we anticipate, it 

 should be well worth while for everyone interested 

 in photography and optics to make a point of 

 attending at least once, and to allow plenty of 

 time to examine and become acquainted with all 

 the latest improvements in objects vended by the 

 photographic and optical trades. 



A New Lens. —By the courtesy of the editor of 

 the " Photographic News," we have recently seen 

 some very remarkable photographs taken by means 

 of anew lens invented by Dr. Griin, of Brighton, 



and under circumstances which in the usual way 

 would be absolutely impossible. For instance,, 

 one of the pictures submitted to us was a ballet at 

 the Alhambra Theatre of Varieties, taken in the- 

 gtth part of a second, whilst the performance was 

 proceeding, and without the knowledge of the-, 

 authorities. The photograph is a distinctly good 

 one, giving an excellent impression of the per- 

 formance, and we confidently assure the inventor 

 that there is a great field before a lens that will 

 accomplish such a result. From what we have- 

 been able to gather about this lens, it would appear 

 to be a combination of glass and liquid lenses. 

 Dr. Griin says it consists of the construction of 

 what is practically a lens of crown glass of great 

 thickness, accurately corrected and free from 

 aberration. Dr. Griin claims for his invention 

 that it is a quicker lens than any other of 

 corresponding aperture. He further mentions that 

 the lens can be made with a greater aperture than 

 that attained by any lens yet known. We believe- 

 the one with which he took the photograph at the 

 Alhambra had a 4-inch focus, with a working- 

 aperture of 2f inches on a J plate used in a hand 

 camera. 



Light in Dark Rooms. — We have often been 

 asked to recommend a safe light to use in the- 

 dark room. To this inquiry there is only one- 

 answer possible. Such a. thing as a •' safe light " 

 is unknown. All we can do is to find the safest 

 light for each type of plate. For instance, a light 

 that is quite safe for a wet plate is useless for an 

 ordinary dry plate ; again, a light that is safe for 

 an ordinary plate is no use for a specially rapid 

 one, and so forth. It therefore follows that the 

 photographer must have at his command a whole- 

 series of tinted glass panes for his lantern, each 

 suitable for developing different plates. For this 

 purpose we have found the most convenient method 

 is to have a fairly large gas or oil lamp, arranged 

 so that the glass through which the light passes 

 can be readily changed and a series of different 

 coloured glasses used. If possible we much prefer- 

 the lamp constructed with a glass tank, containing 

 a saturated solution of bichromate of potassium.. 

 The space between the glasses of the tank should 

 be at least one inch thick, and a gas lamp in which 

 this tank can be inserted will give a most brilliant 

 light all over the room. It will be quite safe for work- 

 ing bromide papers and slow ordinary plates. If it 

 is proposed to develop medium speed plates, then a 

 deep orange glass can be placed in front of the light - T 

 and if extra rapid plates are used, a piece of ruby 

 glass or fabric should be placed in front. Deep ruby 

 colour should be used when isochromatic plates- 

 are to be developed. If it is not convenient to 

 have the liquid tank lamp, then we should recom- 

 mend a lamp with a series of glasses. There- 

 should be one yellow, one orange, one ruby, and 

 one green : these can be used separately or to- 

 gether, just as required. We would suggest also 

 that the glasses should be tested photographically 

 by exposing a portion of a plate to the action of 

 the light for two minutes, at a distance of, say, one 

 foot. The plate should then be developed in 

 darkness, when it will be at once seen, on taking 

 the plate out of the fixing, whether that portion of 

 the plate exposed to the light of the lamp i> 

 affected in- not. Of the above scries of glasses it 

 will be found that the orange and green combined 

 will give a most pleasing light, which i> fairly safe- 

 for ordinary plates and papers. 



