NA TURE 



[November 3, 1898 



r^on under investigation, and the improbability of tliere 

 being a minor planet in that region at that time, it can 

 be quite well understood that such discoveries were the 

 result of an immense amount "f labour. By the use of 

 the photographic method, all these difficulties are at once 

 swept on one side ; for, since the presence of one of these 

 bodiescan only be detected by its own motion relative to 

 the stars around it, the photographic plate can at once 

 indicate this. Further, by using a fairly wide angle lens, a 

 far greater portion of the sky can be examined at one 

 time than was previously the case, and therefore the 

 chance of finding these bodies is considerably increased. 

 We have only to e.vpose a photographic plate in an 

 •equatorialiy mounted telescope driven by clockwork at 

 sidereal rate, then all stars will appear as circular discs, 

 and any minor planet, which, of course, has its own 

 proper motion, will be represented by a small trail, the 

 iength of this depending on the duration of the exposure 

 and the amount of movement of the minor planet during 

 (that mtervaL 



plate searched for are by no means easily seen. The 

 plates, further, must always be carefully washed for some 

 hours, in order to get rid of all trace of the hyposulphate 

 of soda. It is an exceedingly easy matter to quickly • 

 dry photographic plates ; but most methods, even that 

 of the use of alcohol, are inclined to create disturbances 

 in the film, such as unequal contraction, which render it 

 unfit for accurate measurements afterwards. 



Herr Witt therefore waited until the following day 

 before the negatixe was examined. Not only did he 

 find on it the record of the long-lost minor planet he 

 was seeking after, but another one. Althaea (119), which 

 had been previously discovered. With the help of a 

 lens a further trail was noticed, but on account of its 

 unusual length, which was an indication of a quick 

 moving body, he thought at first it must be a comet. 

 To verify this conclusion, the following evening he turned 

 the 12-inch refractor towards the same region, and found 

 in that position a stellar- not cometary-like body oi 

 magnitude 10 to 11. Without any further delay the dis- 



:^l.uuiitg paili ul [11. .V pl.aiet ui ^k) 



At the present day numbers of workers are exposing 

 plates on clear nights to delect both new and old mem- 

 bers of this family, and it was during such a search that 

 Herr Witt, of the Urania Observatory in Berlin, made 

 tlie important discovery of this new planet. 



Since the year 18S9 a certain minor planet named 

 Eunike (183) has never been observed, and it was with 

 tlie intention of photographing this object that Herr 

 Witt turned his telescope, on the night of .-\ugust 13, 

 towards the region of ,3 Aquarii, previous calculation 

 having told him that the planet should be in or near that 

 region, .\fter a two hours' exposure the plate was de- 

 veloped and washed, and left to dry until the next day, 

 when it was carefully examined. It may be asked, why 

 the plate, after development, was not immediately 

 «xaniined? .'\ny one wHio is familiar with such work will 

 know that not only is the film very soft, and therefore 

 easily liable icj be damaged, but that the trails on the 



NO. I 5 14, VOL. 59] 



covery was at once communicated to the " Centralstelle* 

 for astronomical telegrams, and by this means the news 

 was immediately sent to a great number of observatories. 



Curiously enough, on the same evening (.August is) 

 that Herr Witt was fortunate enough to photograph the 

 trail of this planet, Herr Charlois, at the Nice Observ? 

 atory, was photographing the same region (probably 

 with the same intention as Herr Witt . He also securea 

 a record of the presence of this new body. Prof. Per- 

 rottin, the director of the observatory, did not, however, 

 make the discovery known until after Herr Witt's 

 announcement ; nevertheless, although the latter is en- 

 titled to declare himself the real discoverer, both names I 

 should be handed down to posterity, as is the case with 

 the discovery of Neptune by Leverrier and .Adams. 



It was not long, however, before numerous accurate 

 observations of this new body were made, and they ex- 

 tended over a period of days (seventeen in number 



