ON EDUCATIONAL AND DOCUMENTAKV FILMS. 291 



reach the screen. The blinds should be drawn : blinds which pull up from the bottom, 

 running in channels, are advantageous in preventing troublesome streaks of light. 

 The screen may with advantage be surrounded by a curtain extending vertically 

 2-3 ft. from the screen so that the latter is protected from all but weak diffused 

 daylight. Provided the picture is not impaired, the presence of diffused daylight in a 

 room may be considered an advantage, as it lessens the contrast between the bright 

 picture and the surroundings, and thus diminishes liability to eye-strain. Such 

 supplementary illumination also aids the supervision of audiences of children. Small 

 projectors have been shown satisfactorily to audiences of 150 and even 200, provided 

 the room can be darkened and the seats suitably arranged. 



Eye-strain. — Suggestions in regard to conditions to be observed with a view to 

 diminishing eye-strain were embodied in the Report of a Joint Committee appointed 

 in 1919 by the Illuminating Engineering Society at the request of the London County 

 Council. Great importance was attached to undue elevation of the eyes as a cause of 

 eye-strain. It was recommended that the angle of elevation to the top edge of the 

 picture should not exceed 35°. With a screen 3i to 4 ft. square, this angle would 

 probably not be exceeded, provided no seat was nearer than about 7 ft. from the 

 screen. The Committee also advised that the lateral angle of view to the extreme 

 edge of the screen should not exceed 25°. This condition would usually be complied 

 with, assuming a screen of the size indicated above and a minimum distance therefrom 

 of about 7 ft., if the width of the space occupied by the audience did not exceed 20 to 

 25 ft. Compliance with the above conditions would in itself probably prevent undue 

 proximity to the screen rendering difficult the following of movements in the picture. 

 The Committee suggested that the distance of the most remote seat should not exceed 

 twelve times the height of the picture. With a 4 ft. screen this would mean a 

 limiting distance of about 50 ft. 



Attention was also drawn to the importance of avoiding defects in films (scratches 

 or holes in the gelatine), and vibrations due to light and portable apparatus not being 

 securely fixed — all of which may act as possible sources of eye-strain. 



In conclusion, it may be remarked that long-continued observation of moving 

 pictures is liable to impose some strain on the eyes of children. Any danger in this 

 respect may be materially lessened if stationary pictures are shown at suitable 

 intervals. Effective ' colour-interludes,' based on the displaj^ of scenes which undergo 

 gradual changes in colour, have been devised for this purpose. 



D. Stbuctueal Conditions. 



In considering the structural conditions desirable for the use of films in schools, 

 the Committee limit themselves to safety base (non-flam) films. 



As the danger in the use of non-flam films appears to be no greater than in the use 

 of a lantern for other purposes, the suggestions merely amount to precautions which 

 seem desirable when any audience of young people is brought together in a building. 



It should be remembered that until non-flam films have been solely in use for some 

 time the risk of panic will be greater than with most other public displays. This 

 could be combated by the exhibition of a notice that the films are non-inflammable. 



Exits. — The room used should have at least two exits which should not be near the 

 lantern and access to which should be maintained without obstruction. The doors 

 of these exits should open out and be secured by panic bolts which are released by 

 pressure on the doors from within. 



The tops of the doors should bear the word Exit to be visible from all parts of 

 the room, and this should be illuminated by a source of light independent of the 

 lantern. 



Gangways. — Sufficient gangways leading to the exits should be provided free from 

 obstruction. 



Electric Leads. — The leads to the lantern should run so that interference, intentional 

 or accidental, by the audience is not possible. For example, if thej' have to cross 

 the floor a suitable trench with cover should be provided in the floor. These leads 

 should have their own double pole fuses of the enclosed type in a cast-iron box. The 

 arrangements should be such that if the lantern fuse ' blows,' the fuses controlling 

 the lights of the hall will not be affected. If this presents difficulties in a small 

 installation, as an alternative sufficient low voltage lamps served by portable 

 accumulators should be provided to give enough light for emergencies. 



Space. — While no special enclosure for the lantern or operator is necessarj', 



U2 



