764 



NATURE 



[NuvtMUEk 24. 1923 



mount iiiK guard over the spawn, and later protecting 

 the newly-hatched fry from maraudinp visitors (Fig, 5), 



Kit., t. — Ijtrva of tlciithwalcli Iwclle eating into roof-timlien of 

 Westminster Halt. 



is an ideal nature study subject which is bound to 

 rivet the attention of every boy who has the uood 

 fortune to see it. One can but hope that in 

 the near future this class of film may be- 

 come a regular feature in the programme of 

 the kinematograph theatres throughout the 

 countr)', and ultimately replace much of 

 the vulgar trash and sordid themes that at 

 present occupy far too prominent a place on 

 the bill. 



The production of these natural - history- 

 films is by no means a simple matter, for if 

 they are to be of real educational value, not 

 only must the record show the subject clearly, 

 but also they should be taken by, or under 

 the direct supervision of, one who is thoroughly 

 conversant with the habits, characteristic 

 movements, and life-history of the creature, 

 so that no important phase is missed or 

 wrongly interpreted. This the British In- 

 structional Film Company appears fully to 

 have realised, their films having been taken 

 and edited by a band of acknowledged experts. 

 The actual taking of these records of animal 

 life calls for great technical skill and judg- 

 ment and for the exercise of untiring patience, 

 for the difficulties to be surmounted are 

 infinitely greater than in ordinary photo- 

 graphy. Hours of patient watching and 

 waiting have to be faced, and often when the 

 end seems in sight something will happen ; 

 the stock of film in the camera runs out, or 

 the sky becomes too overcast to permit of 

 sufficient light for the extremely short ex- 

 posures necessary, and the final stage is 

 missed — perhaps the last possible chance of 

 the season, and the whole of the work has to 

 be begun all over again the following year. 

 " Light, more light ! " is the constant ptayer 

 of the naturalist kinematographer, for he 

 must be able to obtain sixteen fully exposed 

 little film negatives per second if his record 

 is to give an approximately truthful screen 

 picture ; while to catch every stage in a 

 swift movement like the leap of a salmon or 

 the beat of an insect's wing, the sixteen 

 pictures may have to be quadrupled at least. 



Although the photographic emulsion with which the 



NO. 2821, VOL. 112] 



celluloid film is coated is very fast, the need < 



extremely short exposures renders it ncrr 



employ lenses working at very large 



or F.3, if suflirient light is to rea< 1 



siquently, the depth of field that will be cr ; , 



when working close up to the subject, as o; . - ii., 



when recording the movements of small insects, will be 

 limited practically to a few inches, necessitating con- 

 stant most careful readjustment of the focus, should 

 the creature approach nearer to the camera or elect to 

 move further away ; while owing to the enormous 

 subsequent enlargement of the picture when projected 

 on the screen, every detail must be recorded on the 

 negative film with microscopic sharpness. Last, but 

 by no means least, the subject, if a bird or a mammal, 

 has to be accustomed to the presence, and the sound 

 when in operation, of the kinematograph camera ; this 

 often calls for considerable patience, for all wild 

 creatures are siistjicions of unfamiliar ohi<'rts or sonnd'^. 



Fig. 5. — Nest completed, and female depositing spawn, while mxle guards the nest. 



Even in captivity, this inborn mistrust and uneasiness 

 in the presence of an unfamiliar sight or sound is main- 



