THE use of a camera in the air dates back many years, and some attempts wereactually made as early as 1858, when Mons Nadar successfully took photographs ofParis from a balloon From these initial attempts the taking of air photographshas always made an appeal to the Services both from a Military point of view andfrom the map making aspect

The development of air photography in the British Air Service dates from theformation of the Royal Flying Corps in 1912 Very little progress was made untilthe outbreak of war in August, 1914 At this time the British Air Service wasequipped with a few press type cameras and some simple portable developingequipment From these small beginnings, however, grew the Photographicorganisation of the Royal Air Force which towards the end of the War wasproducing thousands of negatives and prints every day The equipment in use wasnecessarily designed under War conditions, and the personnel handling thisequipment had often to forsake the camera for the machine-gun Thus as a naturalconsequence the equipment, excellent though it was, had not all the refinementand accuracy which is desirable or demanded for survey purposes

It is well known that by employing aero-photogrammetric methods and instruments one is able to produce maps in considerably shorter time and at much lower cost than is possible when the work is done according to the old terrestrial methods This saving of time and money will, however, vary according to whether a sufficiency of terrestrial bases is already known or not For it is, indeed, a fact that in the hitherto practised aero-photogrammetric methods most of the time was spent in finding at least three fixed points for every plate-pair which were recessary to make an exact setting into the plotting instrument possible If such terrestrial measurements have to be carried out in difficult country, for instance in primeval forest areas or extensive swamps, it cannot but happen that the expenditure of time and money will be so greatly augmented that in the end the whole advantage of aerial survey becomes illusory

DR WATTS, in introducing Captain Barnwell, said I am sure we are all very muchindebted to Captain Barnwell for giving us the benefit of his knowledge andexperience The subject cannot fail to be interesting to all who are associatedwith aricraft design, although the attitude of aircraft designers generallyvaries between two extremes On the one hand there are some who consider airscrewdesign as something mysterious, to be left to an outside expert, and on theother hand there are some who consider it so simple that it can safely be leftto an internal subordinate It is quite common knowledge that Captain Barnwelladopts the happy medium, and deals with the subject himself

I remember that 14 or 15 years ago, at the old British and Colonial AeroplaneCompany, Captain Barnwell was designing a special “hush-hush”machine I was a mere nobody in the drawing office, entrusted with airscrewdesign, but I remember that Captain Barnwell designed his own airscrew for this“hush-hush” machine, much to my secret chagrin So behind thispaper there is 14 or 15 years of personal knowledge of airscrew design