Observations on the West Coast of Africa. 479 



ference in instruments and in the interpretation of results. 

 Then again, if it may be assumed that the mean figure of the 

 earth is already known, as closely as the pendulum will give it, 

 research should be carried on by determining local variations 

 of the force of gravity. 



It is evident that extended voyages offer exceptional facili- 

 ties for increasing our knowledge in magnetism and gravita- 

 tion and should be utilized when possible. Such an occasion 

 presented itself in the fall of 1889 when it was proposed to 

 send an expedition to Africa to observe the total eclipse of the 

 sun on December 22. The eclipse party was under the direc- 

 tion of Professor Todd of Amherst College. Through his 

 courtesy, and by authority of Commodore Dewey, Chief of 

 Equipment and Recruiting, U. S. 1ST., the superintendent of 

 the Coast and Geodetic Survey sent one of the assistants to 

 make magnetic and gravity observations. Originally, work of 

 this nature was only proposed for the eclipse station in Angola. 

 It was noticed, however, that on the return trip, several impor- 

 tant stations might be visited without much loss of time, and 

 that these stations had already been occupied by earlier pendu- 

 lum observers. Permission was therefore granted by the Hon. 

 Secretary of the Navy, for the vessel to stop at the Cape of 

 Good Hope, St. Helena and Ascension long enough to enable 

 the Coast and Geodetic Survey representative, to make his de- 

 terminations. In addition to this, stops were made at Barba- 

 dos and Bermuda, and through the kindness of Captain Yates, 

 commanding the " Pensacola," full series of observations were 

 obtained. On the outward trip time was more valuable since 

 it was desirable to "reach Angola as soon as possible. For this 

 reason only magnetic work was attempted at the coaling places. 

 There appear then as the result of the trip fourteen magnetic 

 and eight gravity stations, distributed as follows : Azores, Cape 

 Verde Islands, Freetown in Sierra Leone, Elmina on the Gold 

 Coast, St. Paul de Loanda, and Cabiri, in Angola, Capetown, 

 St. Helena, Ascension, Barbados, and Bermuda. On both 

 St. Helena and Ascension the force of gravity was measured 

 at the level of the sea and at the highest elevation practicable. 

 On the former island Jamestown was selected for the lower 

 point, and Napoleon's residence at Longwood, for the upper. 

 The pendulum apparatus was set up in the kitchen of what is 

 known as Napoleon's new house, now leased by Mr. Deason. 

 At Ascension the sea station was at Georgetown — the other 

 was on Green Mountain. Foster's observations at the latter 

 place show a defect of gravity of two oscillations per day as 

 compared with the sea-level — that is to say, that having cor- 

 rected his oscillations on the summit, for elevation, and for the 

 effect of the mountain, on the supposition that it was solid, he 



