Unusual images that might be related to the early history of aviation.

I recently purchased at a camera auction an Adams Best Bag Changing Box, identical to the one described in this advert printed in "The British Journal Photographic Almanac" dated 1905. To my surprise inside the box there were 5 glass 1/4 plate (4.25 x 3.25 inches) negatives showing outdoor images of 'white circles' on what I believe to be an airfield, as there are a couple of hangars in the distance. The date of the equipment, the use of glass plates and the subject matter lends itself to assume the negatives were created around 1915, a few years before the RAF was created in 1918. I am trying to determine what the white circles could be used for, and if the airfield can be identified. The found negatives have been inverted to create these positives.