August 3, 1900.] 



SCIENCE. 



179 



specially for the purpose by Brashear. The 

 light was thrown into the telescope by a 

 very perfect plane silvered mirror made 

 by Mr. Ritchey for the instrument. The 

 equatorial mounting that carried this mirror 

 was also made under Mr. Eitchey's direction 

 though not for this special purpose. It was, 

 hower, adapted by him for a 48-hour revo- 

 lution. This instrument was driven by the 

 clock from Professor Hale's 12-inch equa- 

 torial. The mounting also carried a 15- 

 inch mirror for Professor Frost's spectro- 

 scopic work. 



A long horizontal tube connected the 

 6-inch objective with the photographic 

 house. This tube consisted of a wooden 

 frame work covered with red water proof 

 paper and was whitewashed on the upper 

 part. A white cloth covering was also 

 placed over it with a few inches of air space 

 between the cloth and the tube. Frequent 

 diaphragms were put along the inside of the 

 tube to prevent stray light or reflections. 



The photographic house in which the 

 plates were to be exposed, was about 30 

 feet by 6 feet ; it was of wood made thor- 

 oughly light proof by heavy red paper. 



The plates were placed in a carrier 15 

 feet long, which ran on ball bearings in a 

 light-tight sheath — the exposures being 

 made through an aperture in the sheath 

 where the image fell. 



With this carrier, by rapidly shoving it 

 along, one plate after another could be sub- 

 stituted for exposure with the minimum 

 loss of time, about four seconds for a change. 

 "With it seven plates were exposed. Three 

 of these were 14x17 inches, and the other 

 four 25x30 inches. The following expos- 

 ures were given these plates. 



No. Exposure. Size ot plate. Kind of plate. 



1 \' 14 X 17 Cramer double-coated. 



2 2 14 X 17 Cramer ' crown. ' 



3 8 25x30 " " 



4 30 25x30 " " 



5 14 25x30 " " 



6 4 25x30 " " 



7 1 14 X 17 Cramer double-coated. 



A stop, regulated by hand, fixed the posi- 

 tion of the carrier at each exposure, so that 

 the image should always fall central on the 

 plate. The plates were all set parallel to 

 the celestial equator. 



The exposures were made by a wooden ex- 

 posing shutter, with a round aperture on one 

 end of it. This shutter was controlled by two 

 cords, one from each end, running into the 

 photographic house. These cords being held 

 taut, one in each hand, the exposures were 

 made with absolute certainty and rapidity, 

 by a quick pull with one or the other hand. 



In the actual work, the carrier contain- 

 ing the plates was moved forwards by Mr. 

 Eitchey after each exposure. At his signal 

 ' ready ' the proper exposure was given by 

 me, the time being counted from a sounder 

 beating seconds. 



The seven plates were exposed without 

 a hitch, the program being successfully car- 

 ried out. 



The signal for the beginning of totality 

 was given by Mr. Putnam of the U. S. 

 Coast Survey, who observed the contacts 

 with a telescope at the Smithsonian Station, 

 a hundred feet or so distant. 



The exposures were begun immediately 

 upon the signal for totality. A signal was 

 also to be given ten seconds before the close 

 of totality. This last signal was heard 

 while preparing for the last exposure, and 

 certainly within three or four seconds of 

 this the exposure was made ; the sun was 

 then just appearing as a small speck of 

 light — the end of totality having apparently 

 come sooner than was expected. 



At each exposure the image was seen on 

 the plate and I was at once impressed with 

 the striking likeness it bore to the corona 

 of January 1, 1889. Though the moon ap- 

 peared very black on the plates, the corona 

 itself was disappointingly feeble. In the 

 casual inspection, during exposure, the 

 prominences were not noticed and but little 

 detail was visible. 



