132 REPORT — 1891. 



2. The size of the plate is immaterial provided that the focos is sharp. Use a 

 magnifier when focussing, and for objects like clouds focus upon a distant tree or 

 building. 

 ■ 3. Use a lens which does not distort the image. 



4. Do not touch up either negative or print. 



5. When photographing any object which is moving or changing, a series of 

 views taken at short intervals, so as to show the progress of the phenomenon, will 

 be of especial value. 



6. Whenever possible, a figure or other object of known dimensions should be 

 introduced, in order to serve as an approximate scale. 



Cloud Plwtographj . 



For heavy clouds no special apparatus is required, but exposure must be shorter 

 than for ordinary landscape work. For very thin clouds exposure must be extremely 

 short and development very cautious. Fair results may then be occasionally 

 obtained without special means. 



In order to obtain better and more certain results three methods have been 

 adopted : — 



(a) Using a slow plate and rapid lens, with short exposure. 



(J) Using an ordinary plate and lens, but with a sheet of pale yellow glass in 



front of the lens, 

 (c) Using an ordinary plate and lens, but placing a plane mirror of black 

 glass in front of the lens, so that its surface makes an angle of about 

 : 33° with the axis of the lens. The image reflected in the mirror is fairly 

 easy to photograph. 



The Committee hope to receive examples of each of these processes, as well as 

 examples and descriptions of any other special devices which may be adopted by 

 observers. 



Lightning Phntograpluj . 



When a thunderstcrm occurs at night it is very easy to photograph the flashes of 

 lightning. 



Fix the camera rigidly (do not hold it in the hand) and expose it to a part of the 

 sky where flashes are frequent. 



As soon as one flash has crossed the field of view change the plate. 



Whenever possible, count the number of seconds between seeing the flash and 

 hearing the beginning of the thunder. Note this time on the print or form. 



If you have two cameras some useful results may be attained by using one as 

 described above and holding another in the hand, pointing in about the same 

 direction, but kept in constant oscillation. It is hoped that two photographs of the 

 same flash may be thus secured. 



Another desirable experiment is to fix both cameras in the same direction, change 

 the plates in one after each flash, but leave the plate exposed in the second until six 

 or eight flashes have crossed the field of view. 



If the camera is placed in a window this must be open, as the interposition of a 

 window pane may give rise to multiple images. 



Be particularly careful to note the exact time and direction of each flash photo- 

 graphed. 



A rapid lens, with a stop ■£ or thereabouts, should be used for lightning. 



Prints, which may be mounted or unmounted, should be sent as early as possible 

 to the Secretary at 



'Waeleigh,' Tulse Hill Pakk, London, S.W. 



This work of distribution has been greatly aided by the courtesy of 

 the Council of the Royal Meteorological Society. But in spite of their 

 assistance the time available for the purposes of the Committee has besn 

 mainly devoted to carrying out this introductory labour and conducting 

 the correspondence it has involved. 



The secretary to your committee has also personally appealed to 

 various societies on behalf of the work in hand by the exhibition of 

 lantern slides in explanation of the Committee's object. 



