Morning journal and courier., 1880-12-25
C,uriosities of the Moon.
Professor Young Before Mechanics and
 Tradesmen i'm Stefnway Hall.

Professor Young Before Mechanics and
 Tradesmen i'm Stefnway Hall.
 Prof c. A. Young delivered very inter esting lecture at Steinway Hall Thursday evening before the General Society of Me- chanics and Tradesmen, the subject being ssThe Moon'' He began by speaking of the importance of that luminary, which is main ly due to it's proximity to the earth, as it is enabled to exert a perceptible influence upon human affairs. It is the principal cause of the tides it affects the magnetic currents of the earth, and perhaps influences the me- neurological conditions to scarcely apprecla- ble degree. It's indirect effects, however, are much greater. The motions of the moon first gave to the ancients the idea of moving un1- verse, and the earliest observations of as- tronomers were conducted upon it. By the records of eclipses which were recorded cen turies ago, we are able to fix the dates of events, and to compare the chronol- ogy of different nations The first recorded eclipse was observed by the Chinese, 2,500 years before the Christian ; and from the year 763 B. G., down to the present time eclipses have been quite carefully recorded. We can fix the date of Herod's death, be- cause it is known that an eclipse occurred on the succeeding night The moon furnished the first practicable method of finding the position of 8 ship at sea- About the year 1715 prize of e200 900 was offered to the first man who would devise a method of de- termining longitude at sea within thirty miles, Observations of the moon afforded 8 means to accomplish this result, for 1t was found possible to calculate the position of the moon in reference to the stars for an hour. However. the moon is not very good time indicator, for, since it takes her thirty days to complete the circuit, it is not possible to measure the slight changes in her position with sufficient accuracy for this purpose; it is like using clock without minute hand only thirty times worse. Nevertheless, In polar expeditions the moon is depended upon for time. because chronometers are not trust worthy in extreme low temperatures. As- tronomy originated with observations of the moon and for about hundred years the mathematicians and astronomers were almost exclusively engaged in studying her motions, actuated, no doubt, by the desire to obtain the prize already mentioned. Newton dis covered the law of gravitation, but he could not have proved it without the aid of lunar observations He calculated the size of the moons orbit. and found that in size and form it agreed with his theory, for it bends in to ward the earth about one-twentieth of an inch in one second.
 The moon, the speaker continued is con tinuaIly getting out of its course, or from five to twenty minutes s.ahead or behind where the theory would place it. The question now to be solved by astronomers is whether some irregularity in the motion of the earth is the cause of tha discrepancy. The interest which is attached to the study of this object is greatly enhanced by the intrinsic beauty of its surface as revealed by the telescope. In this respect the most interesting of the plan etary bodies are the moon and Saturn. The former is full of variety, and constantly changing with the direction of the suns light, and every increase in the power of the telescope reveals something new. As regards the earth, the moon is
 kho., iko fo+i ifc size, as compared with the former, is very much greater than the proportion that exists between the satellites of the other planets. The lunar month is given as 29 days, 12 hours, fl minutes, 2 seconds and 684-1000 of second. The speaker would not fraction. but he stated that the length of the month is probably known to within one-hundredth of second. It is de- termined thus accurately by measuring the time e1apsing between two echpses which are separated by long intervals. The motion of the moon is subject to so many variations that to calculate its exact position for any given time would require four or five hours of steady work, and about 50 different cor 'rections must be applied. This has to be done for every hour in making the Nautical Almanac The shortening of the moons month, which has been observed, IS partly caused by gradual change in the earths or D1I, Wnlcn 1S BroWAnS u1oAO oAloulnh. AAAAo change will continue for about 5e, GOO years longer, after which the process will be revers- ed Laplace made this calculation, but an error was afterward found by Adams which reduced his result by about one-half. Then, the effect of the tides was thought to exert an influence by retarding the rotation of the earth, but still later investigations have shown that the real and the theoretical oscil lations agree very perfectly, and that the l tides do not exert any appreciable influence upon the rotation of the earth.
 As is well known, the moon always pre- sents one side toward the earth. We now see the same face as Calico did when he first looked at it with the telescope. This fact is explained by the supposition that the moon once formed part of the earth, and that when ] the planet was in plastic state the moon was