290 POPULAR SCIENCE MONTHLY. 



will be signalized in tlie history of astronomy by the detection 

 among these little objects of one which has entirely cast into the 

 shade all other discoveries of the same nature. On the night of the 

 13th of August, 1898, a German astronomer, Herr Witt, exposed a 

 photographic plate to the heavens in his telescope in the Observa- 

 tory of Urania, at Berlin. On that plate a picture of the heavens 

 was obtained, and in that picture a new planet was revealed. At 

 first the discovery of one more asteroid does not imply very much. 

 Hundreds of such planets might be found, and indeed have been 

 found, and yet no particular comment has been called forth. But 

 this planet found by Witt is a imique object; it is more interesting 

 than the whole of the four hundred and thirty-two other minor 

 planets which have preceded it — not, indeed, on account of its size, 

 for Witt's planet is a wholly insignificant object from this point 

 of view. The special interest which this new planet has for us 

 dwellers on the earth lies in the fact that it seems to be the nearest 

 to the earth of all the other worlds in space — the moon, of course, 

 excepted. This is the reason why the attention of all who are in- 

 terested in the science of astronomy has been concentrated on 

 Witt's discovery. It is certainly the most interesting telescopic 

 revelation which has been made for many years. 



It may illustrate a characteristic feature in the progress of 

 modern astronomy if I describe how Witt succeeded in obtaining 

 this picture. He had selected one of the most rapid plates that 

 the skilled manufacturer can supply to the photographer. He put 

 this plate into his telescope, and he directed it to the heavens. If 

 that plate had been used in broad daylight for the more ordinary 

 purpose of obtaining a photographic portrait, an exposure of half 

 a second would have been quite long enough. But the very faint 

 stars can not work their charm on the plate with equal rapidity; a 

 second is not long enough, nor is ten seconds, nor even ten minutes. 

 If we desire to secure an imprint of the faintest stars we must 

 expose the plate for an hour, and sometimes for even much longer 

 than an hour. Of course, an exposure of such duration would 

 utterly ruin the picture if a gleam of any other light obtained 

 access. But in the darkness of night the plate is secure from this 

 danger. Each star is thus given time enough to impress its little 

 image at leisure. 



The photographer has often occasion to deplore the poorness 

 of his light. It is, of course, in the endeavor to counteract the 

 poorness of the light that so long an exposure is frequently given. 

 But it will not be any longer supposed that, from the astronomer's 

 point of view, a tedious exposure must necessarily be a disadvan- 

 tage. Let it be henceforth recollected that it was the very require- 



