ASTRONOMY. 35 



elusion that the accounts which remain to us are in no one 

 case sufficient to connect the eclipses computed back from 

 modern data with the phenomenon recorded by the historian. 

 In many cases it is not even certain that this phenomenon 

 was an eclipse at all. 



2. The nineteen eclipses of the "Almagest" give data which 

 are at the best uncertain. 



3. The eclipses of the Arabian astronomers, which are now 

 lor the first time utilized. 



4,5,6. The observations ofTycho Brahe,etc.,of Gassendus 

 and Hevelius, are not valuable for this purpose, as they were 

 taken without the aid of telescopes, and are not of sufficiently 

 ancient elate. 



7. The observations of De la Hire, De l'Isle, and others, 

 from 1072 to 1750, are now discussed for the first time, and 

 prove to be most valuable material. From 1750 to 1860 or 

 1865, Hansen's tables represent the observations well. The 

 whole series is represented by omitting the empirical terms 

 of Hansen depending on eight times the mean motion of 

 Venus. The value of the acceleration from observation 

 alone is 8.8", Hansen's adopted value being 12.17". This 

 value 8.8", however, requires to be changed by 0.9" in a 

 century to satisfy observations, and there are several ways 

 in which this may be effected. The rotation of the earth 

 may not be uniform, the analytical theory may not be com- 

 plete, or other and undiscovered bodies may enter in. A 

 term expressing the total correction to Hansen's tables is 

 deduced and provisionally adopted. Its theoretic basis re- 

 quires further investigation. Dr. Haughton has considered 

 these ancient eclipses in a memoir read to the British Asso- 

 ciation. Dr. Weiler has also a series of papers on the theory 

 of the secular acceleration in the Astronomische Ncichrichten, 

 No. 2060 et seq. 



In 1787 Sir William Herschel announced that he had ob- 

 served three volcanoes in active operation in different parts 

 of the moon, the diameter of the principal crater being about 

 three miles. In May, 1877, Dr, H. J. Klein, of Cologne, 

 while examining the moon, noticed a great black crater on 

 the Mare Vaporum, and a little to the northwest of the well- 

 known crater Hyginus. He describes it as being nearly as 

 large as Hyginus (or about three miles in diameter), as being 



