94 LAUNCHING DATA FOR A BATTLESHIP. 



A microscope was obtained with cross hairs and special rotating gear for the 

 eye-piece. There is a reading circle and vernier that allows readings to 0.25 of 

 one degree, or with the camera pointed directly at the clock to one-twenty-fourth 

 of a second of time when used to determine the position of the clock hand. A 

 mechanical stage, with traverse motions at right angles and with verniers reading 

 to 0.1 mm., was used to hold the film and to read the position of the marks on the 

 vessel relative to the scale, and for other readings. 



Plate 31 is a reproduction of a part of the strip of film exact full size. The film 

 used was a positive, not a negative. Plate 32 is a reproduction of picture No. 428, 

 magnified six diameters. It is one that is included on Plate 31. Plate 33 is a view 

 of the clock from picture No. 428, magnified thirty-one diameters, the magnifica- 

 tion used for reading the film. Plate 34 is a view of station 65 from picture 

 No. 428, showing a reading between 20 and 21 feet on the scale. This view is also 

 magnified thirty-one diameters. The exact reading is obtained by taking for the 

 excess over 20 feet, the proportion of one foot that the distance in millimeters 

 from 20 feet to station 65 measured by the vernier on the mechanical stage, is of 

 the distance from 20 feet to 21 feet measured in the same way. 



Both Plates 33 and 34 are very accurate representations of the exact size and 

 appearance as viewed through the microscope. Half of the clock face was in 

 shadow, and the difference in appearance of the two sides is less than that shown 

 on Plate 32. It was attempted, in making the enlargement, to reduce the difference 

 to that actually appearing when viewed through the microscope. 



The method of plotting the curves, Plate 38, first on distance with a hori- 

 zontal base, next on time, is evident on inspection. The distance traveled, the ve- 

 locity, and the acceleration are all measured in foot-second units along the hori- 

 zontal base drawn at the actual height of the tide at time of launch. To obtain 

 corresponding values parallel to the ways, multiply by the secant of the angle of 

 slope, that is, by 1.0016. The actual observation spots for the distance curve are 

 shown by small circles. A point is obtained for each picture read, and as many 

 points may be obtained as desired. 



The dotted portion of the distance curve before the first picture was obtained 

 as follows: — The initial position of the ship on the ways was known, thus giving 

 an origin of distance but not of time. Points "A" and "B" had been observed 

 independently by stop-watches by observers at the head of the ways, right at the 

 marks where they had an opportunity to get good observations. The known part 

 of distance curve was prolonged back to the known origin of distance and to pass 

 fair through "A" and "B" plotted to the same scale, and the origin of time for 

 "A" and "B" thus located was taken as the origin of time for the whole curve. 



The points plotted as + and X are two independent series of stop-watch ob- 

 servations for time and distance run; they were made according to the method 

 described on page 258, Volume II of Transactions of the Society of Naval Archi- 

 tects and Marine Engineers for the year 1894. The observers were necessarily at 

 some little distance from the ship, in order to see the station marks when the vessel 



