September 2^, 191 7] 



NATURE 



67 



being submersed completely for fifteen hours in a 

 beaker of distilled water free from air, they regain 

 their normal activity within a quarter of an hour of 

 their removal from water. I have not yet tried sub- 

 mersion for longer periods, but the subject is of great 

 interest, and I should be obliged if any of your readers 

 re able to throw any light upon it. 



Henry Cohen. 

 "Avenue House," Petworth Street, Cheetham, 

 Manchester, September 2. 



THE AUTUMN MOON. 



LLWAR theory has become recently an 

 engrossing study for all, and is not to be 

 classed such a useless abstraction as before. The 

 peculiar beha\iour of the autumn full moon in 

 our high latitudes has always attracted the 

 ttention of the hunter and farmer, and given it 

 lie name of harvest or hunter's moon, accord- 

 ing as it comes next before or after the equinox. 



This behaviour, which has attracted attention 



''■ and given the name, will be on view at this full 



[ moon ; it will be noticed how the time of moon- 



•■ise will be very nearly the same during the inside 



: a week, the full moon coming up at sunset, or 



.. little before or after. 



The full moon on this September 30 is, then, 

 strictly speaking, the hunter's moon, but may 

 also be called the harvest moon in this backward 

 season. The previous full moon of September i, 

 coming a month before the equinox, did not show 

 up so clearly to a noticeable extent the peculiarity 

 of a successive rising at sunset, with little or no 

 delay. 



The astronomical explanation is simple. At the 

 autumnal equinox the full moon is passing through 

 the ascending node of the ecliptic at the vernal 

 equinox, and its motion from south to north of 

 the ecliptic is quickest. 



The usual retardation of rising due to the 

 moon's motion along the ecliptic is diminished by 

 the rapidly northing motion, and the effect is to 

 reduce the retardation from an average forty- 

 eight minutes daily in a month of thirty days to 

 something considerably less, especially in high 

 latitudes, where the retardation may sometimes 

 be wiped out altogether, and the moon will rise 

 earlier for a night or two. The same effect of 

 diminished retardation takes place every month, 

 while the moon is moving through the vernal 

 equinox ; but the effect passes unnoticed, as the 

 moon is not full. 



We begin by taking the moon to move in the 

 ecliptic, but her orbit is really inclined at about 

 five degrees, and the nodes of the orbit revolve 

 in eighteen years. The effect is not the same, then, 

 every year, but greater or less ; and the modi- 

 fication can be investigated on astronomical 

 theory from the numerical data of the Nautical 

 Almanac. In some conjunctions it will be pos- 

 sible to see the full moon travel round the horizon, 

 in a latitude five degrees short of the Arctic Circle, 

 as in the northern parts of Sweden. 



The effect is reversed and the retardation of 

 rising is greatest when the moon passes through 

 XO. 2500, VOL. 100] 



the autumnal equinox and is receding most 

 rapidly from the pole star, as in the last old and 

 new mtK)n a fortnight ago. 



The full moon at the vernal equinox will rise, 

 or set, from an hour to an hour and a half, or 

 two hours, later each night, and advantage can 

 be taken if moonlight is to be avoided. 



The words in "Macbeth," "The moon is down 

 . . . And she goes down at twelve. I take 't, 'tis 

 later, sir," would imply a moon about a week old, 

 and moving through the autumnal equinox, mak- 

 ing midsummer the time of the play. Shake- 

 speare's education has been called in question, 

 but he can always be relied upon for accurate 

 observation, and is not content to take his natu- 

 ral philosophy out of a book, second-hand and 

 unverified. 



The moon is full in passing through the autum- 

 nal equinox when the sun is opposite in the vernal 

 equinox — that is, in spring. This full moon will 

 be observed to be very late in getting up and in 

 setting again ; but it has not attracted attention, 

 as unconnected with any influence on human life. 



It may be called Endymion's moon, from the 

 legend of Mount Latmos, where we may suppose 

 Endymion, an astronomer, had built his observa- 

 tory within reach of Miletus. In the legend he 

 drew the moon goddess down by the arts of a 

 Thessafian witch, and in the springtime would 

 not let the goddess go in a hurry. The scene has 

 been utilised by Hardy in "Two on a Tower." 



Mount Hamilton, with the Lick Observatory on 

 it, resembles Latmos in being within reach of 

 San Francisco. The journey there is a favourite 

 pilgrimage and, in contrast to our Greenwich, 

 visitors are encouraged to cheer up the solitude 

 of the staff, and provide merriment after they are 

 gone by ' their innocent questions. One Lund 

 divinity visitor was reported to take a great 

 interest in the life of young Endymion, and 

 curious of his habits, she asked, "What do you 

 do all night?" "We take the observations." 

 " What do you do all day, then ? " " We reduce 

 the observations." "But why cannot you take 

 your observations the right size once for all ? " 



The erratic behaviour of the moon in the sky 

 has been a pitfall for artist and poet; the mis- 

 takes have provided much amusement to the 

 astronomer. Turner, the artist, has painted the 

 sun setting in the east in his picture of the old 

 Tdmeraire. Hogarth's picture of "The Lady's 

 Last Stake," now gone to America, in which Mrs. 

 Thrale claimed to have sat for the lady's model, 

 is intended to draw a moral on sitting up gam- 

 bling all night, with the moon looking in reproach- 

 fully at the window. But the astronomer 

 recognises a winter new moon, and the hour is 

 about five o'clock tea time, so we may imagine the 

 other members will be knocking at the door and 

 asking, "When are you two coming in to tea? " 



We still speak of new moon and old, and so 

 perp>etuate the ancient theory of Pythagoras that 

 the moon is not a celestial body coming round 

 every month, but a sort of magic lantern shown 

 on the sky. This doctrine of Pythagoras is still 



