All these things had to be observed at one and the same time--the moving model itself, the models alongside the jetties, the commotion on the surface, the swayings to and fro of the rods attached to the submerged floats--all, or most of which, at all events, it was impossible to make self-recording. Yet, seeing that it was of the utmost importance that the relations between all these things should be observed, and recorded from time to time as the model was towed along, it is evident that something must be done, and a cunning use of the kinematograph solved the problem quite easily. At various points commanding a good view of the model harbour and its shipping these machines were placed, and so several series of photographs were obtained, by the study of which all the different movements could be seen and compared. A large dial too was rigged up upon the travelling carriage by which the model was towed, a finger on which denoted the distance which the carriage had travelled at any moment. This large dial came into each photograph, of course, and so each picture bore upon itself a clear record of that particular moment in the voyage of the model to which it referred. Thus we see an instance of how the very latest and most up-to-date methods of amusement are sometimes applied to serve very practical purposes. Akin to the experiments upon ships are aerial experiments to determine matters connected with the navigation of the air. At Barrow-in-Furness the great firm of Vickers, shipbuilders and armament manufacturers, and latterly builders of aerial craft for the British Admiralty, have erected a machine for testing the efficiency of aerial propellers and other things of a kindred nature. Upon the top of a tall tower there is pivoted a long arm of light iron framework. To the end of this a propeller can be fixed, so that as the arm revolves there is produced almost exactly the same conditions as those which prevail when a propeller drives an aeroplane or steerable balloon. By means of suitable mechanism the propeller can be turned at any desired speed, with the result that it drives the arm round and round upon its pivot on the top of the tower. The force which the propeller thus exerts can easily be measured, and so can be determined such questions as the most efficient speed for each type of propeller, the power which any particular one can develop, the best form for each particular need, and so on.