300 



SCIENCE. 



[Vol. I., Ko. 11. 



THE FLORIDA EXPEDITION TO OB- 

 SERVE THE TRANSIT OF VENUSA 



In selecting the four stations in the northern 

 hemisphere from which to observe the transit 

 of Venus on Dee. 6, 1882, the probable 

 weather at that season, together with the geo- 

 graphical position of the various points con- 

 sidered, were the principal terms in the problem. 

 It was desirable to find points where good 

 weather would be likely to prevail, and where 

 all the contacts, both at ingress and egress, 

 could be seen. Considerable advantage being 

 gained by increasing the distance between the 

 southern and northern stations, those in the 

 United States were chosen as far north as pos- 

 sible, and fulfil the first two conditions. 



With these views, the transit of Venus com- 

 mission selected a point near Fort Selden, 

 New Mexico, San Antonio, Tex., Cedar Keys, 

 Fla. , and the naval observatory at Washing- 

 ton. The three southern stations, all between 

 29° and 33° N. Lat., presented marked differ- 

 ences in their surroundings. The station in 

 New Mexico was about ojOOO feet above the 

 sea, with the air dry and cool. San Antonio 

 has an elevation of about 600 feet, with a dry, 

 warm climate. Cedar Keys is barely above 

 the water of the Gulf of Mexico. In Novem- 

 ber the weather was hot and comparatively 

 dry, with increasing dampness as the nights 

 became cooler, about the first of December. 

 Washington was chosen because a complete 

 set of apparatus was in working order at the 

 observatory. 



The party under my direction was assigned 

 to Cedar Keys, which point we reached Nov. 4. 

 The name Cedar Keys was formerly applied 

 to the whole group of keys between the mouths 

 of the Suwannee and Withlacoochee rivers, 

 but is now used to designate an active business 

 town on Way Key, the largest of the group. 

 This town sprang into existence after the close 

 of the war, and is chiefly interested in the 

 lumber, shipping, and fishing interests, while 

 it is the shipping-point for all the cedar used 

 by the Faber and the Eagle pencil companies, 

 in the manufacture of pencils, etc. 



A site for the observing station was selected 

 in a small park at the eastern end of the 

 town ; and the construction of the buildings 

 and mounting of the instruments were pushed 

 forward as fast as possible. The so-called soil 

 of Way Key is simply a mass of white sand ; 

 and in the grounds of the station, where a pipe 

 well, with a pump, was sunk, the sand existed 

 at a depth of at least fifteen feet. 



1 Abstract of a paper read by Prof. J. R. Eastman before the 

 Washington philosophical society, March 24, 1883. 



The Ijuildings for the protection of the 

 instruments were a transit-house, photograph- 

 house, and the building to contain the equato- 

 rial telescope ; while a small storehouse was 

 built to protect the stores, etc. The principal 

 instruments were a portable transit, a 5-inch 

 equatorial telescope, and a photoheliograph. 

 The first two require no description. The 

 photoheliograph consists of an objective of 5 

 inches aperture and about 40 feet focus, a 

 heliostat for throwing the sun's rays on the 

 objective, and a plate-holder at the focus of 

 the objective. The objective and the mirror 

 of the heliostat are mounted on the northern 

 pier at northern stations, and the plate-holder 

 is mounted on a similar pier in the photograph- 

 house. The accessory apparatus consists of 

 a measuring-rod, permanently mounted, for ac- 

 curately measuring the distance from the ob- 

 jective to the photograph-plate ; a movable 

 slide, with a slit of adjustable width for expos- 

 ing the plates ; and a circuit connecting with 

 the chronograph in the transit-house, so ar- 

 ranged, that when the exposing-sHde is moved 

 to expose the plate, and when the centre of 

 the slit is opposite the centre of the plate- 

 holder, the circuit is broken, and the record 

 made on the chronograph. A black disk is 

 painted on the north side of the slide, and so 

 placed, that when the sHde is at rest at one end 

 of its course, and the image of the sun is ad- 

 justed concentric with this disk, it will fall on 

 the centre of the plate-holder when the slide is 

 moved. When all the adjustments are made, 

 the exposing of the plates is quite a simple 

 matter. The image of the sun is thrown by the 

 heHostat upon the black disk and centred, 

 the sensitive plate is fixed in the plate-holder, 

 the operator moves the exposing-slide, and the 

 time of exposure is recorded on the chrono- 

 graph. The plate is now read^' to be devel- 

 oped ; and here the ablest photographer has an 

 ample field for the exercise of all his skill. 

 The first photographs were made Nov. 23. 



The weather was excellent till the last of 

 November, when we had our first norther and 

 a frost, followed by rain and another norther ; 

 but Dec. 4 and 5 were clear and mild. At 

 sunset on the 5th, a low bank of clouds was 

 spread along the south-western horizon ; but 

 the sky was clear at midnight. On the morn- 

 ing of the Cth, the southern and eastern sk}' 

 was nearly covered with light cirrus and stratus 

 clouds, with an upper south-west wind, while 

 the surface wind was from the east. All the 

 apparatus was examined, and found to be in 

 good order ; and the astronomers went to the 

 equatorial telescope to observe the first contact. 



