1889.] XEW YORK ACADEMY OF SCIENCES. 51 



south of the equator. The horizon is therefore only 9^ inclined 

 to the axis of the earth. These facts enable Prof. Todd to ar- 

 range his instruments on a novel plan. The apparatus used for 

 photographing the transit of Venus can also be used in photo- 

 graphing an eclipse. It has been so used ; but it is troublesome 

 to set up and to adjust properly. The United Scates expedition 

 will discard all the apparatus except the 38-foot-focus lens and 

 the camera-box. The lens will be screwed into the end of a 38- 

 foot-long iron tube, at the other end of which is the photo- 

 graphic plate; on this plate will be formed an image (when the 

 telescope is properly directed to the sun) four and a quarter 

 inches in diameter. It is proposed by Prof. Todd to mount this 

 long telescope as a tripod, — the telescope being one leg of the 

 tripod. A second leg will have its foot resting in a close-fitting 

 cylinder filled with dry sand ; the cylinder will be supplied Avith 

 a faucet for allowing the sand to escape. The whole apparatus 

 is to be placed in such a position that the telescope will be 

 pointed to the sun at the instant of totality ; then, on allowing 

 the sand to escape from under the third foot of the tripod, it is 

 hoped that the telescope will follow the sun in its diurnal mo- 

 tion westward. Experiments made with the apparatus in Wash- 

 ington under Prof. F. H. Bigelow's charge, seemed to indicate 

 that the apparatus could be readily handled and adjusted. 



In the United States expedition, — for the first time, I think, 

 — an attempt will be made to make all exposures automatically. 

 Prof. Todd will place several photo-telescopes on a single polar 

 axis, driven by a large clock. 



The chances for cloudy weather on the African coast are great, 

 — said to be one-half. Understanding this, Prof. Todd has ta- 

 ken with him a number of scientific men interested in branches 

 other than astronomy, who will be able to bring back important 

 results. Prof. Cleveland Abbe represents the United States 

 Signal Service, and will make a special investigation of ocean 

 air-currents. He carries with him on the ship some two thousand 

 small balloons, — or rather the rubber skins and the apparatus 

 for making hydrogen gas and filling the skins so as to make 

 balloons about twelve inches in diameter. These are to be var- 

 nished and properly tagged, and then allowed to escajjc from 

 the ship every two hours ; they drag one hundred and fifty feeC 

 of thread. Tlie air-curient will carry them away, and after a 

 while those that do not colla{)se may be caught in some ship's 

 rigging, captured and sent to Washington, with tag and date as 

 to when and where found. It is lioped that material will thus 

 be obtained to give new information of value about ocean air- 

 currents. 



The Coast Survey Ofiice sends Mr. Preston, an experienced 



