i\W. I, 1877] 



NATURE 



Is 



who was contemporary with Apollonius, refers to a total 

 eclipse of the sun which had recently occurred, and 

 remarks of total solar eclipses in general that " a certain 

 effulgence is seen round the circumference," so that 

 although the sun may be wholly covered by the moon 

 " still the eclipse is deficient in duration as well as in 

 amplitude," this surrounding effulgence not allowing of a 

 very intense shadow. These remarks of Philostratus and 

 Plutarch Prof. Grant thinks may probably apply to the 

 same eclipse, and afford "the earliest allusions to the 

 corona recorded in history." Several attempts have been 

 made to discover the date of the phenomenon, but so far 

 as we know without success. 



The earliest distinct and more accurate account of the 

 corona is that given by MM. Plantade and Capids, who 

 observed at Montpellier on the occasion of the eclipse of 

 May 12, 1706. 



The Outer Satellite of Mars. — Our ephemeris of 

 the satellite of Mars is here continued ten days further 

 from the elements employed last week, though much 

 greater difficulty must now attend observations than when 

 the discovery was first announced. In the middle of 

 August the distance of the planet from the earth was less 

 than o"4 ; on November 12 it will have increased to o'68. 

 At the next opposition in 1879, the least distance of Mars 

 will be o*482, at a north declination of upwards of 18°, so 

 that observations may be made at many observatories in 

 this hemisphere, probably without greater difficulty than 

 about the late opposition ; at the following one in 

 December, 1881, the planet will attain a declination of 27° 

 N., but its distance from the earth will be at no time less 

 than o'6o2. 



Prof. Asaph Hall's complete discussion of the observa- 

 tions of the satellites of Mars, made in the present year, 

 will be looked for with much interest ; it is only fitting 

 that this investigation should be left in the hands of their 

 discoverer, who has made the year 1877 a very notable 

 epoch in the history of practical astronomy. 



The following positions of the outer satellite are for 8h. 

 G.M.T. 



Nov. 3 ... Pes. 358 ... Dist. 21 

 ,, 4... ,, 69... „ 52 

 „ 5... „ 122... „ 25 

 „ 6... „ 236... „ 42 

 „ 7... „ 272... „ 37 



De Vico's Comet of Short Period.— The year to 

 which we drew attention some time since (i876"9-i877'9) 

 as one which might possibly witness the re-discovery of 

 De Vico's comet of 1844 is drawing to a close without its 

 having been remarked, and the chance of detecting it at 

 this season if the perihelion passage be not already 

 passed, is small. We must therefore probably place the 

 comet in the class which, though undoubtedly moving in 

 elliptical orbits of small dimensions when under observa- 

 tion, are now " lost." Whether in the case of De Vico's 

 comet this arises from a larger error in the determination of 

 the mean motion ini844than at present appears admissible, 

 or whether the action of the planet Mars, to which allu- 

 sion has been made in this column, may explain it, or 

 again, whether the comet has encountered one of the 

 minor planets, and thereby been deflected or disintegrated, 

 cannot be at present ascertained. It was hardly to have 

 been anticipated that the laborious investigations of Prof. 

 Briinnow relating to the motion of this comet from 1844- 

 55 would not have resulted in its re-observation. 



METEOROLOGICAL NOTES 



Mean Atmospheric Pressure of Europe. — A 

 great contribution to this very important subject has 

 been made by Dr. Buys Ballot in the second volume of 

 the " Nederlandsch Meteorologisch Jaarboek voor 1872," 

 which has just been published. The first 130 pages of 



the volume are occupied with a very careful and in certain 

 directions exhaustive discussion of the barometric obser- 

 vations made at about no places situated in different 

 parts of Europe from 1774 to 1874. The method of dis- 

 cussion is identical with that adopted by Dr. Buys Ballot 

 in his recently published paper on the Meteorology of 

 Holland (Nature, vol. xvi. p. 89). This method consists 

 in accepting as the normal mean atmospheric pressure at 

 Greenwich, Vienna, and Palermo, the arithmetic means 

 of the observations made at these places which embrace 

 periods of 100, loi, and 84 years respectively. The 

 normal values for the other stations have been determined 

 by the process of differentiation, that is, by a comparison 

 of the means of all the observations made at the place 

 with the corresponding means of one or more places at 

 the nearest available stations whose normals have been 

 already determined, and thereafter applying the necessary 

 correction. Thus the normals which have been arrived 

 at in this very laborious manner are substantially the 

 averages which would have been obtained if the obser- 

 vations at each of the stations had been made during 

 precisely the same terms of years. The thirty years' 

 averages should probably have been accepted as the best 

 normals for Stykkisholm in Iceland, instead of correcting 

 these averages from the Greenwich and Christiania 

 observations, seeing that a low average barometer at 

 Stykkisholm is frequently coincident with a high baro- 

 meter at either or both of these stations, and vice versd. 

 The resulting differences, however, are but slight. This 

 work of Dr. Buys Ballot, particularly when looked at with 

 reference to future discussions, may be said to take a 

 place at once as a classic of meteorology. The next step to 

 be taken in this field of European meteorology is the discus- 

 sion of all good barometric observations made in Europe 

 during the meteorological lustrum ending with 1875. To 

 the results of this discussion corrections could be applied 

 from Du Buys Ballot's normals, which are sufficiently 

 numerous for the purpose, and thus a graphic representa- 

 tion could be made of the closest possible approximation 

 to the true mean atmospheric pressure of Europe. In 

 this way, by disclosing the striking, and in a large 

 measure still unrecognised, influence of large masses of 

 land and water on the barometric pressure, much light 

 would be thrown on the origin and history of those great 

 atmospheric currents which, flowing or sweeping over this 

 continent, are mainly instrumental in determining the 

 climates of its different regions. 



Meteorology of New York, U.S.— The "Annual 

 Report of the New York Meteorological Observatory for 

 1876" gives, in addition to the individual observations 

 made daily, and their monthly and annual averages, a 

 more than usually full statement of rain and wind obser- 

 vations. On pp. 39-88 are given the details of the 

 amount of rain and snow-water which fell each hour 

 from 1870 to 1876, together with the hourly averages of 

 each month for these seven years. These hourly means 

 show maximum amounts during winter, from 11 A.M. to 

 3 P.M. ; during spring, from 9 P.M. to i A.M. ; during 

 summer, from 5 to 10 P.M. j and during autumn, from 

 3 to 8 A.M. The irregularity of these periods and the 

 irregular occurrence of secondary maxima indicate that 

 seven years is too short a time for the determination of 

 the hourly curve of the rainfall at New York. There 

 appears, however, a tendency to a double maximum 

 varying considerably with season. Extended observation 

 alone can give this curve. The influence of the daily 

 fluctuation of temperature and of the sea breeze which 

 sets in very decidedly from south-east during the hot 

 months on the rain-curve, can then be studied. During 

 the same seven years the duration of each shower has 

 been noted in the number of minutes, the average 

 result of which is that the minimum time of fall, a 

 small fraction less than two days, cccurred in June ; 

 from this time it slowly but steadily rose to 3 days 



