28 PROCEEDINGS OF THE AMERICAN ACADEMY. 



on Forbes Hill in Quincy, at a height of 128 feet above the aviation 

 field (141 feet above mean low water), and the other on the estate of 

 Mrs. E. M. Carey, in Milton, at a height of 71 feet. The length of 

 the base line (QM upon the map, Plate 1) was 6236 feet. The stations 

 were visible to each other, and, although the grandstand was visible 

 from neither, aeroplanes could be observed as soon as they had risen 

 to the height of 50 or 75 feet. 



The position of the base was selected so that observations could not 

 at any time be interfered with by the sun, and that the angle of eleva- 

 tion could be measured without an eye prism up to an altitude of more 

 than 15,000 feet above the center of the field. 



The distance from the field was not so great that it was necessary 

 to read the angles with great accuracy, while it was sufficiently great 

 to reduce materially the difficulty in following the rapidly moving 

 aeroplanes, so that it was possible to observe quickly and accurately 

 both horizontal and vertical angles without a finding device. 



The instruments used were a special theodolite by C. L. Berger 

 reading horizontal angles to 10" and vertical angles to 20", and a Buif 

 mining transit reading both horizontal and vertical angles to 20". 

 Both instruments had full vertical circles, and inverting eyepieces 

 magnifying about thirty diameters. 



Through the kindness of Mr. Carl Keller, the New England Telephone 

 Company connected the two end stations and the central station at the 

 field during the entire period of the meet. 



It was thus possible to insure simultaneous observations at the two 

 stations in both coordinates. That they were practically simultaneous 

 is clearly shown by the tables which follow, in which the approximate 

 times are given as noted at each station. Where the times differ it is 

 almost always possible to make an exact agreement by altering one or 

 both by a single second, so that the mean of the times would rarely be 

 in error by that amount. 



The error of the observers' watches was found by a telephone com- 

 parison with the official chronometer on the field immediately before 

 each flight. 



By combination of the observations we were able not only to compute 

 the altitudes of the aeroplanes at intervals of forty seconds or less, but 

 also to locate their corresponding positions as projected vertically on 

 the ground plane, and thus to plot so many points of the spiral both 

 in ascent and descent as to form an interesting and useful record of all 

 the details of the flight. 



It may here be remarked that the use of this method seems prefer- 

 able to any that requires the aviator to attain his maximum height at a 



