JOHN JACOB BAEYER. 265 



quested, and to show the impoi-tance 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 1869, 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. No 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 formula 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 empei'or 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. Helmcrt, Baeyer's successor as 

 President of the Prussian Geodetic Institute, his sketch of the scientific labors of Baeyer, 

 an excerpt from " Yierteljahrsschrift der Astronomischc Gesellschaft," Band 2, Eeft 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 theoretischen Gradmessungs-Arbeiten," an ap- 

 pendix to the report of the Permanent Commission for 18S1. A revised edition of this 

 valuable publication will appear in connection with the report for 1886. 



