A headteacher attending a conference on ‘Children and the Cinema’ at the British Film Institute in 1946 observed that,
Here you have in the cinema a medium for mass entertainment as well as mass education, and I do not think you can separate those two much. They are so intertwined and linked with one another that you cannot see where entertainment ends and education begins. 
Secrets of Nature arguably contributed to this intertwining more than any films of the interwar period, rendering distinctions between ‘education’ and ‘entertainment’ practically meaningless. Their scripts never missed an opportunity to produce laughter, and the advent of sound saw the Secrets adopt a light-hearted and jocular tone, accompanied by up-beat music and narrations. The fact that the films were frequently shown as part of conventional evening cinema programmes demonstrates that they were treated by many viewers as entertainment. Secrets were usually played alongside other light-hearted ‘shorts’ in advance of the main feature, and were often listed alongside Disney cartoons. The producers behind the Secrets films were not always consistent about how they envisaged the position occupied by their films on the education/entertainment spectrum. On the whole, however, they were seen as principally entertainment films. As Mary Field expressed it in 1941, ‘every film was alive and vital, full of drama, was utterly unscientific, and each carried out the originator’s aim — to interest people in the world of nature about them. In short, they were grand entertainment.’  But the films also had educational potential – the production company in charge of making the Secrets, was afterall, called British Instructional Films, and showbiz only partly explains their popularity.
The line between instruction and entertainment film had long been contested, and the Secrets were not out of the ordinary in their attempts to simultaneously promote laughter and transmit scientific knowledge. As Luke McKernan has established, Charles Urban, who first employed F. Percy Smith during the 1910s, had great ambitions for cinema to be adopted as an educational tool, and excitement regarding the medium’s pedagogical potential was widespread throughout the early twentieth century, especially in Britain, the US, Germany and France. The ‘Visual Education’ movement, as its proponents were known in the US, made enthusiastic claims about the capability of cinema, but also radio, and later television, to communicate knowledge. As one proponent, G. Patrick Meredith would write in 1946,
Through these media we can bring before the child vivid reproductions of objects too large, too small, too distant or inaccessible to be seen directly, thereby extending his experience; we can emphasize important features so as to bring out their significance; we can show how moving parts work and present growth, change, motion at controlled rates; we can symbolize arrays of facts and their inter-relations in easily comprehensible patterns which stimulate thought and argument. 
Film was ideally positioned, therefore, to represent scale, growth, change and motion – all crucial to the understanding of subjects like the life sciences and natural history. The notion of ciné-biology, developed by the Secrets team built on this concept by articulating precisely what the camera could add to the practice and representation of biology. W.M. Warden, a lecturer in Biology at London’s Institute of Education, noted the medium’s value for instruction in the life sciences:
Apart from the scientific value of such records, a strong appeal is made to children by watching the movements of living things. […] In still pictures there is always the danger that the observer fails to appreciate the dynamic quality of living things. One of the greatest revelations the film has to make in this respect is the demonstration of this dynamic quality in plants which are too often thought of as static. 
William Percival Westell, the director of the Letchworth Museum and a renowned popular naturalist, was convinced of the ability for natural history films to educate the pupblic about the natural world. Westell even used natural history films and lectures to directly challenge what he viewed as the dangerous influence of Hollywood on his local cinemagoing audience. In his evidence to the 1917 Cinema Commission of Enquiry, he observed:
As regards the films which I have exhibited, the least appeal is made generally by pond and marine life, insects, snakes and lizards; and the films which have made the most appeal to children have been the birds, which seem to quite fascinate them, and the light fairy story, which is, of course, absolutely the tit-bit of the afternoon. […] The grown-ups, without whom I could not carry on the entertainment, appreciate plants, industries and birds, and they also do not like the wriggly creatures, especially if it is, say, a water beetle devouring a worm in a tank, which they say is horrible. 
Film was seen as an ideal medium to appeal to young impressionable minds, and numerous experiments were conducted during the interwar years which sought to demonstrate the cinema’s pedagogical powers (a future blog post will look at some of these in detail). In 1932, the report of the Commission on Educational and Cultural Films produced its report, The Film in National Life, which led to the creation of the British Film Institute, which would establish committees of teachers to advise on the making of instructional films. Certainly there were objections to the educational uses of film, on the one hand from sceptical teachers, and from groups of concerned adults who associated film, and especially Hollywood movies, with crude depictions of violence and sex. In this respect, Secrets of Nature was part of a broader project which attempted to make film more ‘respectable’ in the eyes of the British establishment, which increasingly viewed mass media technologies like film as a potential tool for promoting a new style of modern citizenship. These technologies, as Tom Rice has shown, were also deemed to be of use in promoting British imperial interests in its colonies during this period.
In many ways, the popular success of the Secrets films served as advertisements for their educational applications. Afterall, these films were costly to make, and the revenue from cinema halls was critical to ensuring that the series could endure. The fact that their signature style and format was widely recognisable helped tremendously when it came to convincing teachers about their educational potential. Indeed, H. Bruce Woolfe, who originated the idea for the series, was optimistic that one day the ‘non-theatrical’ market would become far more influential – and lucrative – than commercial entertainment cinema.  Nevertheless, the Secrets‘ educational aspects could also prove to be a setback, especially when it came to pleasing audiences at a time when cinema attendance was booming. As one observer wrote, ‘Children do not want to recall associations with the schoolroom on Saturday morning; they do not want films which adults imagine to be wholesome.’  One newspaper report from 1927 noted that many cinema owners were ‘shy of showing these pictures – scared, apparently, by their educational aspect’. On the whole, however, the Secrets appear to have successfully navigated this boundary by leaning closer to entertainment than instruction, but still offering novel natural-historical experiences for many of their viewers.
As the demand for educational films increased in the 1930s, and the Secrets team transferred to a new home at Gaumont-British Instructional to make Secrets of Life, they also began producing a series of strictly educational films under the direction of Julian Huxley, H.R. Hewer and J.V. Durden. But as Field would admit, the two projects were often confused by the public, who saw them as part of the same endeavour. By this time, it had become more difficult to display ‘educational’ films in mainstream cinemas: the 1927 Cinematograph Films Act, which introduced a ‘quota’ for British-made films and was intended to shore up domestic film production, excluded educational and educational and scientific shorts, and gave producers a further incentive to keep the Secrets entertaining. Already from the late 1920s, the Secrets had begun to come under scrutiny, both from scientists who complained that they were ‘unscientific’, and from teachers who complained that they were unsuited to classroom environments. In many cases, the Secrets team began to make two versions of every new release: one aimed at general audiences which used their usual humorous style, and another where the commentary was more explicatory and was intended for educational purposes.
But from the 1930s, they increasingly sought the advice of teachers, including the London Teachers’ Assocation and individual teachers with scientific experience, like Clotilde von Wyss, who helped to adapt many of their films into visual learning aids. However, even these films drew upon the signature Secrets style by appealing to the entertainment value of many of their images, and reviews from the Monthly Film Bulletin by Madeline Munro, an experienced science educator who would later work with Mary Field in making films for the British Council, could be scathing of these qualities – a fixed boundary between education and instruction remained elusive.
 Children and the Cinema. A report of a Conference organised by the British Film Institute & National Council of Women (BFI, June 1946)
 Mary Field, ‘Secrets, 1919-1940’, Documentary Newsletter (Jan 1941)
 G. Patrick Meredith, Visual Education and the New Teacher (1946)
 W. M. Warden, ‘Films in Nature Study and Biology’, School Nature Study, No. 135, Vol 34 (1939)
 National Council of Public Morals, Cinema: Its Present Position and Future Possibilities (1917)
 Evidence of Mr. Bruce Woolfe, Board of Trade, Committee on Cinematograph Films, 30 June 1936.
 Richard Ford, Children in the Cinema (1939)
Angelo Van Gorp, ‘“Springing from a Sense of Wonder”: Classroom Film and Cultural Learning in the 1930s’, Paedagogica Historica, 53.3 (2017), 285–99.
Jennifer Peterson, ‘Glimpses of Animal Life: Nature Films and the Emergence of Classroom Cinema in the 1920s’, in Learning with the Lights Off: A Reader in Educational Film, ed. by Dan Streible, Marsha Orgeron, and Devin Orgeron (Oxford and New York: Oxford University Press, 2012).
Luke McKernan, Charles Urban: Pioneering the Non-Fiction Film in Britain and America, 1897-1925 (2015). Also his website on Charles Urban.