150 



SCIENCE. 



[N. S. Vol. XIX. No. 473. 



DISCUSSION AND CORRESPONDENCE. 



THE LUNAR THEORY. 



In a recent number of the Monthly Noiices 

 of the Royal Astronomical Society, Mr. P. H. 

 Oowell gives an account of his investigations 

 on the motion of the moon. He finds con- 

 siderable errors in Airy's theory, but gives no 

 explanation of the small defect in the tables 

 of Hansen. A curious result of several in- 

 vestigations is to shovsr the accuracy of the 

 tables of Damoiseau, made four score years 

 ago, and after a theory which has gone out 

 of use. 



The interest now shown in the lunar theory 

 by several astronomers promises to give us 

 better tables of the moon. Two methods can 

 be followed. The attractive one is to make 

 a new theory, since in this case one has the 

 entire question in hand. But this requires a 

 great expenditure of labor. The other method 

 would be to correct the tables of Hansen. The 

 accuracy of the coefBcients in these tables is 

 very great, and it is a pity so much good work 

 should be lost. In determining the orbit of 

 the moon for the formation of his tables 

 Hansen introduced twelve unknown quantities 

 into _ his equations of condition, or fourteen, 

 if we include the two depending on the dis- 

 tance from the center of figure to the center 

 of gravity of the moon. It is not much won- 

 der that a small error should have been com- 

 mitted in such a complicated theory. The 

 manuscript of Hansen must be preserved, 

 probably in the observatory of Gotha, where 

 he spent most of his life. There are several 

 astronomers in Germany who studied with 

 Plansen, and who understand his methods. 

 It is to be hoped that a careful revision of 

 Hansen's calculations on this theory will be 

 made and that his error may be discovered. 



After looking at some of the works on this 

 theory I venture to make this suggestion : that 

 astronomers should unite on a system of 

 notation for the lunar theory. So many 

 changes have been made that it is almost 

 necessary to have a dictionary of symbols in 

 order to read the various memoirs. 



A. Hall. 



Norfolk, Conn., 

 January 5, 1904. 



THE SCAURS ON THE RIVER ROUGE. 



To THE Editor of Science : The earth's rota- 

 tion causes in the winds of our hemisphere a 

 tendency to deviate to the right of straight 

 ahead in whatever direction they are flowing 

 (Davis' 'Meteorology,' p. 101). It ought to 

 produce the same effect on rivers (Russell, 

 'Rivers of North America,' p. 41). Instances 

 have been supposed to be found in the streams 

 on the south coast of Long Island (American 

 Journal of Science, 1884, p. 42Y), in the 

 great detrital cone of Lannemezan, on the 

 Rhine, Danube, Ob, Irtish, Nile, New Zealand 

 streams, Parana and Paraguay by authors 

 cited in Penck, ' Morphologic der Erdober- 

 flache,' pp. 351-360. Prom objections that 

 have been made to most of these illustrations 

 it appears that there is more of unanimity as 

 to the theory than in the conviction aroused 

 by the evidence offered. 



The Michigan rivers have long seemed to 

 me suitable to examine for evidence of this 

 sort. They are young, meandering streams, 

 not usually encountering ledges, but flowing 

 either in lake clays or in a till that has few 

 large boulders and is fairly homogeneous. 



The Rouge is a stream some twenty-five 

 miles long that flows into the Detroit River 

 a few miles west of Detroit. At Dearborn 

 two forks of the river unite into one. Early 

 in November I visited the west branch in com- 

 pany with Mr. Isaiah Bowman to look over 

 the availability of the valley for work with 

 my class in field geography. The river is 

 ten or fifteen feet wide, meandering on a flood 

 plain two or three hundred feet wide, which is 

 incised in the level clays that once formed the 

 floor of Lake Maumee. Every now and then 

 the stream in its meandering undercuts the 

 bank, causing a naked bluff of clay in a land- 

 scape that is elsewhere well grassed. Such a 

 bluff is what the Scotch call a scaur. ' As the 

 scaurs indicated the points where the river is 

 actually at work widening its valley, it was 

 proposed to measure the proportion of bank 

 occupied by them. To this end we paced the 

 distance along the river bank under each scaur 

 and by the flood plain to the next one, noting 

 whether the scaur was on the right bank or 



