ASTRONOMICAL PHENOMENA AND PROGRESS. 



53 



ameter, and without either nucleus or well- 

 defined boundary. 



The observed acceleration of this comet's 

 motion has generally been ascribed to the re- 

 sistance of an ethereal medium. This hypothe- 

 sis, however, has not been confirmed by recent 

 researches. According to Prof. Otto StruVe 



Dr. von Asten's calculations show that the last 

 three revolutions of this comet can be perfectly rep- 

 resented by a uniform mean motion, without the 

 hypothesis of a resisting medium, and even with 

 greater precision than all the previous observed re- 

 turns with that hypothesis. At the same time, dur- 

 ing more than one revolution, something like accel- 

 eration has been indicated, and nearly to the same 

 amount as Encke had supposed. This was the case 

 between 1862 and 1865. Again, in other revolutions, 

 as between 1845 and 1848, the acceleration has been 

 subjected to very considerable changes. In the 

 actual state of his researches, Dr. von Asten is in- 

 clined to conclude that the existence of a resisting 

 medium is not proved by the motion of Encke's 

 comet, and that the observed acceleration in several 

 returns ought to be attributed to the action of other 

 forces; for instance, repulsive power produced by 

 the approach, of the comet to the sun, the effect of 

 which might vary considerably, according to the 

 conditions in which the return to the perihelion 

 takes place. 



Winnecke's comet of short period, which 

 had last been visible in 1869, was detected by 

 M. Borelly, at Marseilles, on the morning of 

 February 3d. This is the third return of this 

 body since the discovery of its periodicity in 

 1858. It passed its perihelion on the 12th of 

 March. 



Meteors. At the instance of M. Leverrier, 

 the French Association for the Advancement 

 of Science not long since adopted a systematic 

 plan of observation at the principal meteoric 

 epochs. This plan was attended with marked 

 success on the occasion of the August shower 

 in 1875. At a majority of the observing sta- 

 tions in France the condition of the atmos- 

 phere was highly favorable from the 9th to 

 the llth of the month. At Rouen and Roche- 

 fort the Perseids were seen in considerable 

 numbers on the 9th, though the maximum did 

 not occur till the night of the 10th. At Avi- 

 gnon 858 meteors were recorded between 8 h - 

 35 m> P. M. and 3 h> 40 m ' A. M. The greatest num- 

 ber, however, was counted at Lisbon, Portu- 

 gal, where 1,227 were recorded in five hours 

 and twenty-five minutes, commencing at ten 

 o'clock. It seems highly probable, as M. Wolf 

 has remarked, that the August shower is rap- 

 idly advancing toward a maximum. The phe- 

 nomenon will therefore be lookejl for with 

 more than ordinary interest in 1876. 



Meteors in unusual numbers some as bright 

 as stars of the first magnitude were observed 

 in England on the night of August 5th. Their 

 radiant was near Omicron Andromedae. 



The Iowa Meteorite of February IZth. The 

 American Journal of Science, for November, 

 1875, contains a paper by Prof. N. R. Leon- 

 ard, on an extraordinary shower of meteoric 

 stones which fell a few miles east of Marengo, 

 Iowa County, Iowa, at about 10 o'clock, on 



the evening of February 12, 1875. In the 

 States of Missouri and Iowa the meteor was 

 seen throughout a region extending at least 

 400 miles in length and 250 in breadth. Rev. 

 E. B. Taggart, of Washington, Iowa, describes 

 the body before its explosion as of a u horse- 

 shoe shape, greatly elongated ; the outer edge 

 very bright, then a narrow dark space, with a 

 cone of intense brilliancy, so vivid as to blind 

 the eyes for a moment. It had not a comet- 

 like train, but a sort of flowing jacket of flame. 

 Detonations were heard, so violent as to shake 

 the earth, and to jar the windows like the 

 shock of an earthquake." 



The products of the meteor's explosion were 

 scattered over a tract about seven miles long 

 and from two to four miles wide. The frag- 

 ments varied in weight "from a few ounces 

 to 74 pounds, aggregating, so far as found, 500 

 pounds weight," of which Prof. Leonard se- 

 cured more than 300. The specific gravity of 

 the aerolite was found by Prof. J. Lawrence 

 Smith to be 3.57. 



Diameters of the Planets. The following 

 values of the apparent diameters of the plan- 

 ets, reduced to the earth's mean distance from 

 the sun, and of their true diameters in Eng- 

 lish miles, are given in Nature for June 24, 

 1875: 



They are founded, in every case, upon the meas- 

 ures which, from observational circumstances, ap- 

 pear to deserve the greatest weight, and in the re- 

 duction to true values the solar parallax is taken 

 8". 875, and Clarke's diameter of the earth's equator 

 is adopted. It would, of course, be idle to attempt 

 to offer final numbers, where the difficulties attend- 

 ing observations and the differences between the re- 

 sults of the most experienced and favorably-circum- 

 stanced observers are so considerable : 



In fixing upon the apparent diameters of the bright 

 planets it has been desired to adopt values which 

 shall represent the actual arc values that are pre- 

 sented by the true diameters at the earth's mean 

 distance. Many observations would assign larger 

 values, but undoubtedly less trustworthy for com- 

 puting real dimensions. 



Prof. NewcomVs Researches on the Ura- 

 nian and Neptunian Systems. The great 26- 

 inch telescope of the Naval Observatory, 

 Washington, has been successfully used by 

 Prof. Simon Newcomb in observing the sat- 

 ellites of Uranus and Neptune, and thus ob- 

 taining more trustworthy elements of these 

 remote planetary systems. The satellites of 

 Uranus all move in the same plane, and their 

 orbits are very nearly circular. Their dis- 

 tances and periods are : 



