322 MEMOIRS OF THE AMERICAN ACADEMY. 



following years there are only half as many, and the series itself terminates soon 

 afterwards. The record at Plymouth is more consistent with a maximum than a 

 minimum. No auroras were observed at Upsal in 1733, 1734. and 1735, but none 

 also were observed in 1738, the year of the next spot>maximum. In St. Petersburg 

 the number of auroras had declined from thirty-six to six, but only six were seen also 

 in 1729. If the influence of the secular change, which raised up a secular maximum 

 in 1730, could be eliminated, the residual phenomena might be more consistent 

 with the fluctuations in the solar spots. 7. A spot-maximum is assigned to the 

 year 1738. In Italy an aurora-maximum comes one year earlier. In France no 

 auroras are recorded between 1737 and 1750. In Holland forty-two auroras were ob- 

 served in 1738, but more in 1736, 1739, and 1711. In Germany no auroras were 

 observed in 1738, but thirteen in 173G, and eleven in 1739. In Wittemberg one 

 aurora was observed in 1738, eight in 1737 and 1743. and eleven in 1742. In Plym- 

 outh as many auroras were seen in 1738 as in 1742, but not so many as in 1730, 1737, 

 1739, and 1741. In Lincoping the maximum number of fourteen falls upon the 

 year 1738, but the number sinks to two the following year, the series coming to an 

 end. Twelve were seen at that place in 1734. In Upsal auroras appeared in large 

 numbers in 1739, 1740, 1742, 1743, and particularly in 1741, but none in 1738. 

 In St. Petersburg the number of auroras increased from seven in 1738 to twenty- 

 nine in 1742. In America no auroras were seen in 1738, but five in 1741. 8. The 

 spot-minimum of 1745 comes next under examination. In Italy only two auroras 

 were seen in that year, still fewer in the preceding and following years, but six 

 in 1750. The minimum in France conveys no meaning as it existed for twelve 

 years. In Wittemberg only one aurora was seen in 1744. 1745, and 1746, and 

 none in 1749, though the latter year is so near the spot-maximum of 1750. In 

 Germany the auroras decreased after 1739, but there were fewer in 1742, 1743, and 

 1744 than in 1745, and thirteen in 1746. In. Holland there is a very decided mini- 

 mum in 1744 and 1745. The small number of auroras registered by Musschenbroek 

 in the year 1740 is probably to be explained by his change of residence from Utrecht 

 to Leyden. In Zwanenburg the minimum of 1745 is unchallenged. In Plymouth, 

 also, a satisfactory minimum falls upon the same year. In Upsal there is a minimum 

 in 1744, though fifty auroras were seen in 1746. In St. Petersburg only one aurora 

 was seen in 1744 and 1745, but only one was seen in 1749, and ten in 1746. There 

 were six observed at that place in 1747. The minimum at Cambridge in 1745 and 

 1744 is unqualified. 9. The next spot-maximum is in the year 1750. In Italy there 

 seems to be also a maximum of auroral display. The same is true of Wittemberg. In 



