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PnoTo*fiRAPHic Observations of Comet C, 1902. 



John A. Miller. 



Comet c (Perriiie) 1902, was photogra plied here on every clear night 

 from October 5 to October 22, clouds preventing either earlier or later 

 ones. With few exceptions two photographs were made on each night. 

 One photograph being made with a portrait lens built on the Petzval 

 system, but afterward refigured by Brashear. This lens had an aperture 

 of twelve centimeters and a focal length of fifty-five centimeters. The 

 other photograph was made with an old "tintype" lens which Mr. W. A. 

 Cogshall rescued from a photograph gallery here and which performs 

 surprisingly well. This lens has an aperture of 5.5 centimeters and a 

 focal length of twenty-two centimeters. 



The tail of this comet was exceedingly faint, so faint that it was witli 

 difficulty that it could be photographed at all. Each of the photographs 

 showed two streamers, a long one nearly straight and a shorter one more 

 sharply curved. The greatest length of the short tail was shown on the 

 photograph of October G. It was then l.°S long, while on October 22 it 

 did not exceed one-half degree in length. On October 5 the long streamer 

 subtended 3.°2. Each succeeding photograph showed the streamer longer 

 until on October 22 it subtended an angle of S.°4. In the following table 

 I have shown the results obtained by measuring five of the photographs, 

 which represents fairly well the behavior of the comet. 



In tliis table T is the central time of oxi)Osure; L, the length of the 

 long tail in degrees; S, the length of the short tail in degrees; N, the num- 

 ber which when multiplied by the cosine of the angle between the direc- 

 tion of tlie comet's tail and the radius vector from the sun to the comet 

 gives the length of the long streamer in terms of the mean distance of 

 the earth from the sun: 



