Obscuration of a Lunar Crater. 445 



extent of the whitish spot in the place of " Linne," is greater 

 than the diameter given above. Upon comparing " Linne " 

 with the standard spot, ' ' Dionysius " — the diameter of which 

 as given by Lohrinann, is 13"8 English miles, and also as 

 measured on Rutherford's photograph — the magnitude — that 

 is, the ratio in size, which " Linne " bears to " Dionysius/' 

 reckoned as unity — is O40 ; while on Dec. 15, 1866, its mag- 

 nitude was 0*79, this will give 10*9 English miles for the 

 extent of the whitish spot over the crater, which is exceeded by 

 5*3 miles. Lunar observers will doubtless watch the locality 

 with great interest, especially as at the time when the ter- 

 minator was near the spot, it was quite invisible. Whatever 

 the cause of the obscuration may be, it is to be hoped that 

 the first indication of the returning visibility of " Linne " 

 may be made public, so that the period of its concealment 

 may be well determined. 



Closely allied to the observations of Herr Schmidt, is a series 

 by the writer of this paper. Between the years 1858 and 1863 

 when the Sun had attained a considerable altitude above the 

 Mare Grisium, a white ill- defined cloudy patch was regularly 

 observed a little W. of the well known crater " Picard/-' but 

 it was not seen about the time of sunrise or sunset at Picard. 

 Nothing appeared to throw any light upon this appearance 

 until the year 1863, when in the neighbourhood of the cloudy 

 patch, a little before sunset, a small pit-like marking was 

 noticed. In the year 1864 the attention of Mr. Ingall was 

 arrested by a spot 6° or 7° of brightness in this locality, and 

 towards the end of the year, the cloud-like patch had nearly 

 faded out. On December 12, 1864, Mr. Knott, at his observa- 

 tory, Woodcroft, Cuckfield, Sussex, examined the locality with 

 his 7^-inch Alvan Clark, and discovered two minute craters, 

 I C mu "- and I C mU5 of the new nomenclature. It was some time 

 before this discovery was confirmed, as the smaller crater I C ma 5 

 was very difficult to catch; at length, towards the end of 1865, 

 Mr. E. Bird of Birmingham, saw the pair with his silvered glass 

 mirror, the writer having previously seen them at Cuckfield, in 

 October, 1865. 



It is extremely difficult to say if these craters were really 

 new, still the facts are sufficiently interesting to induce a very 

 careful scrutiny in the neighbourhood of u Linne," especially as 

 from the observation of Schroter there is reason to believe that 

 the crater has suffered two obscurations within a period of 80 

 years. 



Upon receipt of Herr Schmidt's letter to the writer, a 

 translation of which we give below, the Moon Committee of 

 the British Association issued a circular, calling the attention 

 of astronomers to the interesting fact recorded in it. It is 



