A NEW CRATER IN THE MOON 



423 



Every student of the moon knows the craters 

 Copernicus and Eratosthenes. Copernicus lies 

 on the tip of the imaginary nose of the " man in 

 the moon" (that is, of the " face " imagined in 

 the moon, not of the imagined figure of a man 

 with bundle of sticks and dog), and has been 

 compared to a mighty carbuncle there. Eratos- 

 thenes lies a little higher on the ridge of that 

 feature. In the above map the region shown is 

 inverted, to correspond to what the telescopist 

 sees ; it is only necessary to hold the page upside 

 down ! to see the craters in the position they 

 actually occupy on the moon's face. Hyginus is 

 a much smaller crater than either Copernicus or 

 Eratosthenes, but is equally well known to stu- 

 dents of the moon on account of the great rift 

 which passes through the crater, extending out- 

 side in the directions shown by the straight lines 

 in the little map. 



When examining this part of the moon's sur- 

 face with a 5|-inch telescope, on May 27, 1S77, 

 Dr. Hermann J. Klein, of Koeln, observed a cra- 

 ter in the position shown by the small black dot 

 in the above map. At the time of observation 

 the moon had passed her third quarter by rather 

 more than half a day, and the floor of the crater 

 was in shadow. Thus it appeared black. It 

 seemed to be nearly as large as Hyginus, or 

 nearly three miles in diameter. Klein describes 

 it as deep and full of shadow, and forming a con- 

 spicuous object on the dark-gray Sea of Vapors. 

 " Having frequently observed the region during 

 the last few years, Dr. Klein felt certain that no 

 such crater existed in this region at the time of 

 his previous observations." He communicated 

 his discovery to Dr. Schmidt, of Athens, who 

 assured him that this crater was absent from all 

 his numerous drawings of this part of the lunar 

 surface. It is not shown in the maps made by 

 Lohrmann and by Beer and Madler, nor does 

 Schroter, or any of the older lunarians, indicate 

 a crater at this part of the moon's surface. 



Further observations showed that the crater 

 either has no wall or a very low one. It appears, 

 in fact, to be only a deep conical opening in the 

 surface. Soon after the sun has risen it takes 

 the appearance of a dark-gray spot, with an ill- 

 defined edge. Later still, it assumes the same 

 general tint as the Sea of Vapors, and can no 

 longer be distinguished. 



1 Sometimes erroneous directions are given for 

 this purpose ; for instance, to invert the picture and 

 also look at it behind or at its reflection in a mirror. 

 But it is in reality sufficient to invert the picture. 

 This at the same time alters it right and left. 



It will be obvious that this case is not, at a 

 first view, so striking as that of the crater Linne. 

 It is proverbially difficult to prove a negative. 

 In the case of Linne, a crater which had not only 

 been marked in maps by different observers, but 

 had been definitely described by them as very 

 deep, was found to be either missing altogether 

 or at least very shallow. If it had not been for 

 the doubts suggested by Schroter's observations, 

 it would have seemed as though nothing could 

 be clearer than the proof of change in such a 

 case as that. On the other hand, in the case of 

 the crater observed by Klein, before the occur- 

 rence of change can be regarded as proved we 

 must have decisive evidence that the crater did 

 not exist before. The only evidence we have is 

 that it had never been seen before. Now, the 

 knowledge that an object has not been seen may, 

 under certain conditions, amount almost to moral 

 certainty that it did not exist ; and what we have 

 to determine, in the present instance, is the 

 weight of the argument from probability, based 

 on the failure of Schroter, Lohrmann, Beer, Mad- 

 ler, Schmidt, and others, to recognize the crater 

 during their multitudinous observations of the 

 moon. It will be understood, of course, that we 

 have not the direct evidence of any one of these 

 observers in favor of the non-existence of the 

 crater before the year 1877. Not one of them 

 has recorded that, having carefully searched the 

 region inclosed between the two branches of the 

 great rift through Hyginus, they ascertained that 

 there was no crater there exceeding — let us say 

 — half a mile in diameter (smaller craters not being 

 recognizable with the telescopes they used). If 

 they had, the negative evidence would be as satis- 

 factory and decisive as the best positive evidence. 

 All we know is, that in none of their observations 

 did they take notice of a crater in that particular 

 position. 



Unquestionably it would be very remarkable 

 if all these observers had omitted to notice a cra- 

 ter really existing where one now assuredly ex- 

 ists. It is true, craters so small as this one are 

 exceedingly numerous in the moon. And the 

 chance of any crater escaping notice on any par- 

 ticular occasion is no doubt much greater than 

 those unfamiliar with the study of the moon 

 might opine. Many seem to think that on any 

 night in the year the astronomer can study any 

 crater on the moon except on one night per lunar 

 month, when the moon is " new." But in reality 

 the occasions when a crater can be well seen are 

 not by any means numerous. Take, for instance, 

 the "new" crater, if so it must be considered. 



