JOHN JACOB BAEYER. 265
quested, and to show the importance of such an undertaking, he pub- lished a pamphlet on the " Size and Figure of the Earth," giving an account of the geodetic work up to that time, and outlining what re- mained to be done under the auspices of the proposed commission. The permanent commission held its first session in Berlin in 1864, with Baeyer as president — a young organization with a leader aged seventy. The Prussian Geodetic Institute, established in 1809, was also placed under the direction of Baeyer. In both institutions he took an active part, not only in the official routine, but in making astronomic obser- vations and comparing standards until 1874.
Under his instructions, the observations of Bessel at KOnigsberg in 1826, and Schumacher at Guldensteiu in 1829, with the pendulum, were repeated, to see if the length of the seconds pendulum had re- tained the same relation to the toise. Xo change was found, showing that no alteration had taken place in the toise from molecular action, as had been feared.
As a careful observer, his attention was always directed toward pos- sible sources of error in his work, especially toward atmospheric re- fraction, and, as connected with it, the physics of the atmosphere. He utilized all data obtainable from leveling for deducing a formula in which the coefficient of refraction could be given as a function of time or meteorologic conditions. The elaborated fonnula was published in 1840, and with revisions in 1860. He also conceived the application of the converse principle, from which observations for refraction would reveal the condition of the atmosphere. In addition to his purely practical discussions he wrote several articles upon winds, and the solutions of spheroidal triangles. He was an active or honorary mem- ber of the leading scientific societies at home and abroad ; many dec- orations were conferred upon him by various crowned heads. On the 8th of January, 1883, he celebrated the seventieth anniversary of his connection with scientific work. And on the 6th of November of the following year, in honor of his ninetieth birthday, the Academy of Sciences of Berlin sent a deputation to carry their congratulations and good wishes; the Geodetic Institute presented him with a bust of him- self, and the emperor and crown prince sent their compliments.
He brought his interest in scientific work down to his death-bed, on which, two days before his end, he was listening to the report of operations that he had shortly before planned and started. On Sep- tember 10, 1885, the inflammation of the lungs, from which he had suffered only a few days, proved fatal.
Note.— While preparing this, I received from Dr. Helmert, Baeyer's successor as President of the Prussian Geodetic Institute, his sketch of the scientific labors of Baeyer, an excerpt from " Vierteljahrsschrift der Astronomische Gesellschaft," Band 2, Heft 1, to which I am indebted for many facts of interest. A list of Baeyer's writings can be found in " Literatur der praktischen und theoretischcn Gradmessungs-Arbeiten," an ap- pendix to the report of the Permanent Commission for 1881. A revised edition of this valuable publication will appear in connection with the report for 1886.