350 



SCIENCE- GOSSIP. 



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



EXPOSURE TABLE FOR APRIL. 



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

 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 waj-, 

 plates of a higher speed number will require proportionatelv 

 less exposure. 



Time, 10 a.m. to 2 p.m. 



Between 9 and 10 a.m. and 2 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 



1^0 



P. 22 



F. 32 



F.45 



1 



F.64 



1 

 4 



Sea and Sky . . 



30C 



2T0 



lio 



Open Landscape 

 and Shipping 



1^. 



-h 



h 



A 



I 



\ 



\ 



1 



Landscape,with 

 dark fore- 

 ground, Street 

 Scenes, and 

 Groups 



■35 



_i_ 



I 



1 

 4 



\ 



1 



2 



4 



Portraits in 

 Rooms 



V 



4 



8 



16 



32 



- 



- 



- 



Light Interiors 



4 



8 



16 



32 



1 



2 



4 



8 : 



Dark Interiors 



1 



4 



1 



2 



4 



8 



16 



32 



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. — The "Process 

 Year-book " for 1901-2, jjidDlished by Messrs. 

 Penrose & Co., of London, shows a marked advance 

 upon its predecessors. It is full of beautiful 

 pictures, reproduced by the photography of colour 

 and ordinary plain process-work. Some of these 

 are exquisite in artistic production and accuracy. 

 There are many useful articles, on various subjects 

 connected with photography. The " International 

 Annual of Anthony's Photographic Bulletin " for 

 1902, being vol. xiv., is to hand. It is produced 

 in- New York, the London agents being Messrs. 

 Iliffe & Sons, Limited. It is published at the 

 price of two shillings, and contains many illus- 

 trated articles. Some of the pictures are" excep- 

 tionally beautiful, and most of them are interesting. 

 The book will be found useful to amateurs, as well 

 as to the more advanced photographers. Messrs. 

 Penrose have also sent their illustrated catalogue, 

 which contains much information. The annual 

 number of " PhotograiDhy," published by Iliffe & 

 Sons, is beautifully illustrated by a series of the 

 chief photographs of the year. The Thornton- 

 Pickard Catalogue for 1902* contains several im- 

 portant novelties, one of them being the Focal 

 Plane Automan, which is fully described. It is a 

 distinct ad^iance towards obtaining perfect pictures. 



London Geological Field Class.— We under- 

 stand that the annual series of Saturday afternoot 

 excursions of the London Geological Field Class, 

 conducted by Professor II. G. Seeley, F.R.S., com- 

 mences on April 26th, when a visit will be paid to 

 Erith. The excursions will be continued on each 

 succeeding Saturday, except on the Saturdays 

 before "Whitsuntide and in Coronation week, until 

 July 12th. These excursions will afford the means 

 of examining some of the greater movements 

 which the rocks of the SoutJi-east of England 

 have experienced in foldings which changed their 

 level. The denuding action of the sea in levelllng- 

 the land will be examined and compared with the 

 action of atmospheric denudation, as seen in the 

 forms of the parallel hill ranges and valleys of 

 Surrey and Kent. The work of the session will 

 illustrate the geological structure of the districts 

 known as the Weald and the London Basin. The 

 strata examined will comprise all members of the 

 Neocomian and Cretaceous groups, the Lower 

 London Tertiaries, and the gravels and brick earth 

 of the Thames Valley. Opportunities will be given 

 for collecting fossils from these strata, and from 

 the Upper Oolites, upon which they rest. Further 

 particulars can be obtained from Mr. R. Herbert 

 Bentley, the honorary general secretary, 43 Glou- 

 cester Road, Browuswood Park, X. 



Coccus OP the Orange-tree. — This year I 

 have noticed a greater number than usual of those 

 small dark scales on the rind of oranges which 

 when examined with a pocket lens bear so striking- 

 a resemblance in shape and general character to a 

 •mussel-shell with its convex side uppermost. I have 

 been much interested in examining these curious 

 relics of creatures whose life-history is so markedly 

 dissimilar to all other known orders of the animal 

 creation. These singular creatures belong to the- 

 order Hemiptera, and are closely allied to the- 

 aphides. They belong to the Coccidae, the same 

 family as those great pests of the horticultm-ists,. 

 the "mealy bugs," the cochineal insect, - Coccus- 

 cacti," of so much mercantile value for dyeing pur- 

 poses, being also of the "same genus. Carefully 

 removing from the orange with a needle one of 

 these scales, and placing it under the microscope, 

 concave side upwards, we usually find the shell is 

 more than half full of oval pearl-like eggs, probably 

 forty or fiftj^ in number, and one wonders how 

 they got there. Singular to say, while the uni- 

 \ ersal law of Nature appears to be progi-essiou 

 towards perfection, here we find the exception,, 

 in that the female coccus becomes more and 

 more imperfect as she approaches the com- 

 plete state. Having arrived at maturity she 

 selects the place where she intends to feed, then 

 once for all inserts into the plant leaf, stem, or 

 fruit her proboscis, which cannot afterwards 

 be again withdrawn, and there she remains, de- 

 stined for the future to be simply an animated 

 stationary suction-pump. Henceforth she gradually 



