REPORT OF THE SECRETARY. 29 



and Dr. Kane is due to the fact that iu both expeditions the greater 

 portion of the observations were made by Mr. August Sonntag, well 

 known to sciejiee by his previous labors in astronomy and physics. 

 By his early death the expedition sustained a great loss, since through 

 his aid still greater additions would have been made to our knowl- 

 edge of the regions explored. 



Included in the first part of the reductions is also an account of 

 the pendulum observations, intended to furnish information as to the 

 relative intensity of the force of gravity, and, consequently, of the 

 figure of the earth. The pendulum used in these observations is a 

 simple bar of brass, five feet seven three-fourth inches in length and 

 one inch and four-tenths in breadth, and seven-tenths in thickness, 

 weighing nearly twenty-two pounds. It is furnished with two steel 

 knife-edges, placed at 14.2 inches from either end, so that it may 

 be vibrated first with one end downward, and then with the other, 

 afibrding in each position a series of independent observations. The 

 direction of the face of the pendulum could also be reversed, by means 

 of which the results of their regularities of the knife-edge could at 

 least in part be eliminated. 



For comparison of the observations which had been made in the 

 arctic regions, a series was instituted, previous to the sailing of the 

 expedition, with the same pendulum, at the Harvard Observatory, in 

 Cambridge, by the late director, George P. Bond. The result ob- 

 tained by the comparison indicates a smaller value for the polar de- 

 pression of the earth than that deduced from all previous pendulum 

 observations in the northern region. If combined with these, it will 

 bring the resulting figure of the earth nearer to that previously de- 

 duced from the measurement of arcs of the meridian in various parts 

 of the world. 



The compression, as deduced by Mr. Schott from all the observa- 

 tions of the expedition under Dr. Hayes, is -jy-a part of the polar ra- 

 dius. The excess of the number of vibrations in a day at Port Foulke, 

 over the number made by the same pendulum in the same time at 

 the Harvard Observatory, was 129^. The observations were cor- 

 rected for the height above the level' of the sea, for the expansion of 

 the metal on account of variation of temperature, and other devia- 

 tions from a normal condition. It is highly desirable that the same 

 pendulum be vibrated at several points on the eastern coast of the 

 United States, as nearly as possible, under the same meridian as Port 

 Foulke, in order to obtain a series of independent determinations of 

 the curvature of the earth; and for this purpose the instrument has 



