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��COMMENT AND CRITICISM. LiEOT. CoaNWELL, who is to carry on the series of latitude observations at the U.S. naval observatory, referred to ic a previous number of Science (vol. v. p. 60), has recently retnrned from an interview with Professor Oom, the director of the observatory at Lisbon. A list of eleven stars has been selected, and the de- tails of the work have been agreed upon. But two stars will be observed in a night, eauh star being observed east and west of the meridinn before the succeeding star is taken up. Some Bfteen or twenty observations of each star will be made during the year. With the exception of a LjTae, the stars range from the fourth to the sixth magnitude, and the greatest zenith distance at which any star will be observed at Washington is not greater than twelve or thirteen degrees. It is proposed to erect an azimuth mark for testing the stability of the instrument ; and a careful determination of the level will, of course, be made with everj- obser- vation.
��This question of the variability of latitudes is one of considerable interest. Theoretically, periodical changes of latitude may occur, and an examination of observations made at a number of northern observatories during the past seventy-five years — Konigsberg, Milan, Naples, Paris. Pulkowa. and Washington — a|)pears to confirm the existence of such changes. At Pulkowa, which furnishes the most careful aeries of observations, a diminu- tion of the latitude of 0.23", equivateut to about twenty-three feet, is indicated between the years 1843 and 1872; but in all these cases the vari- ations are small, and we must lie extremely cautious in ascribing them to actual changes of latitude. A series of observations made ftt Willet's Point by young engineer officers,
1.128.-1886.
��under the direction of Gen. Abbot, also ap- pears to have some interest and possible bear- ing on the question. By these observations a diminution of ninety-five feet is shown in the latitude since 1880 ; but here, again, it is quite possible that this apparent change may be due to errors of observ'alion. Pergola's plan of making a careful series of observations at pairs of observatories, in about the same latitude, but differing considerably in longitude, will, if thoroughly carried out now, go far towards enabling us to give a definite answer to the question fifty years or more hence.
��The American engineer of May 8 contains an article on the levee system of river improve- ment which demands notice from all who wish the line between fact aud fiction to lie sharply drawn. The case presented is briefly this : the Misaissippi-Kiver commission. Id 1888, as- serted that they had restored the levees along the Yazoo front so as to exclude overflow Dvm the head of that basin, and that as a conse- quence the height of flood at Vicksburg was about five feet lower in 1883 than it had been in 1882; and upon this assertion of facts the commission based an ailment for the general construction of levees along the Mississippi as a means of channel improvement. The flood of 1884 came, and rose three inches higher at Vicksburg than it did in 1882, thereby com- pletely overthrowing all the ailment of the commission,
lu the article referred to, ' J. B. J,' quotes from later reports of the commission proof that the commission had not restored the levees along the front in question in 1883, nor had il been done in 1884. Unless the clearly implied charge that this misstatement was wilful is successfully met by the members of the com- mission who signed the report of 1883 (General Comstock did not), it would seem that the
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