LAUNCHING DATA FOR A BATTLESHIP. 93 



observations with a regular moving-picture camera using standard film and taken 

 exactly as for a moving-picture exhibit. The camera was mounted on the gallery 

 of the adjoining building slip, at a known height and known distance out and 

 known distance from the ways on which the Oklahoma was launched. Its axis, 

 unfortunately, was pointed at a considerable angle instead of normal to the verti- 

 cal plane through the launching ways. It was inclined both downward and toward 

 the head of the slip, as will be seen from the distortion shown in the photographs. 

 The distortion increased appreciably the work of obtaining correct readings. 



A scale graduated in feet was erected on the framework on the opposite side 

 of the building slip about 126 feet from the camera. The marks on the scale are 

 two inches wide. A large clock, with 18- inch dial, was altered to run at approxi- 

 mately sixty times its normal speed, so as to indicate minutes and seconds instead of 

 hours and minutes. The escapement was replaced by a fan regulator to secure 

 steady motion. The clock was suspended at a distance of 15 to 20 feet from the 

 camera in a position such that the clock, the scale, and a part of the vessel would 

 show in each picture. The short focus of the lens allowed the clock, the scale and 

 the ship all to cut sharp. 



Marks were placed on the ship at known stations, as at the 19-foot waterline, 

 and at frames 5, 15, 25, etc. These marks, 3 inches wide, were painted in black on 

 the white bottom paint, and were identified by large numerals also painted black. 



The clock, which had been previously rated, was timed with a stop-watch for 

 five minutes just before the launch and again immediately after. The rate was 

 satisfactorily constant, and was applied in determining the time plotted on the 

 curves. 



The taking camera was started on a signal received two minutes before the 

 hydraulic trigger was released. The vessel did not start promptly and the oper- 

 ator stopped and thus lost the actual start of the vessel; moreover, some of the 

 pictures at the beginning of the film were cut off and not furnished, so that the 

 first picture and the first observation spot are after 6.8 seconds from the start when 

 the vessel has moved 7.33 feet. The film consists of 695 pictures, taken approx- 

 imately sixteen a second ; the actual rate is found to vary generally 6 per cent over 

 or under, and at times as much as 20 per cent over or under. 



After several trials it was determined that a low-power microscope is the 

 best means for reading the film. It was found to give accurate results, and it 

 can be used by an individual at his convenience. The pictures cannot be held station- 

 ary on regular moving-picture projectors on account of the extreme heat, and ordi- 

 nary magic lanterns do not give sufficient light. Trial was made on a special 

 lantern that gave satisfactory light and magnification, and that allowed the picture 

 to be held indefinitely without being affected by the heat. It was found, however, 

 that the pictures were not distinct when viewed from close to the screen, and as that 

 method required electric current, a large dark room and an attendant to be avail- 

 able, the microscope method was preferred. 



