ON MAGNETICAL AND METEOROLOGICAL OBSERVATIONS. 151 



by the zeal and interest of his numerous correspondents, been extended to 

 no fewer than eighty stations. Their publication has been continued or pro- 

 vided for up to the end of 1843, but owing to some difficulties which have 

 unfortunately since interfered and which are understood to have thrown a 

 serious obstacle in the way of their future publication by the Academy, it is 

 greatly to be feared that the course of this series of valuable records may be 

 suspended or abandoned, to the great regret of every meteorologist. 



The magnetic and meteorological observations made at the Royal Obser- 

 vatory at Greenwich, under the direction of the Astronomer Royal, during 

 the years 1840 and 1841, have been printed by order of the Admiralty, in 

 full detail, uniformly with the astronomical observations made at that great 

 national establishment, but in a distinct volume, and it is understood that the 

 subsequent observations will be presented to the public in a like liberal form. 

 The volume is prefaced with a valuable introduction from the pen of the 

 Astronomer Royal, describing every part of the apparatus and the mode of 

 using it. One important characteristic of this station, as it now exists, is the 

 apparatus for observing the atmospheric electricity, a department of meteo- 

 rology of equal importance and difficulty, and which has hitherto been very 

 inadequately studied. 



The diminution of magnetism in steel needles by time as well as by tempera- 

 ture, has been made the subject of a short but valuable treatise by Professor 

 Hansteen, ' De Mutationibus quas subit Momentum Virgae Magneticae 

 partim ob Temporis partim ob Temperaturse Mutationes,' which, although 

 printed in 1842, has only come to our knowledge since the date of our last 

 report. The inquiry into the temperature corrections, being matter o{ expe- 

 riment, is easy in comparison with that of the changes effected by time, which 

 are matter of pure observation, and partake therefore of all the disadvantages 

 which affect purely observational sciences. The conclusion which Professor 

 Hansteen draws relative to this part of the subject is, that the decrements of 

 intensity/ form a geometrical series when the time increases arithmetically, and 

 that the magnetic moment continually approaches to a fixed limit, to attain which 

 of course an infinite time is necessary, but which, practically speaking, would 

 appear to have been approached with a higher degree of approximation, at 

 least for the great majority of cases (seven out of nine) which have formed 

 the basis of Professor Hansteen's conclusions within two or three years from 

 the epoch of their magnetization, and in some instances much more speedily, 

 according to the hardness of the steel and other causes. 



Dr. Lamont, director of the observatory at Munich, has published a 

 summary of the results of the observations made at that station during the 

 years 1840, 1841, and 1842. Of these, the declinations previous to June 

 1841, and the intensities previous to November in that year, are regarded by 

 him as of inferior value to those subsequent to those respective epochs. The 

 daily fluctuations of the declination and of the horizontal intensity, deduced 

 from the assemblage of the monthly means obtained during the available 

 portions of these years, and of the mean declination from 10 to 10 days 

 during the whole period (which he considers to be unaffected by those causes 

 of uncertainty which affect the hourly observations during the earlier por- 

 tion of it), are tabulated and graphically projected. In the projection of the 

 daily fluctuations of the declination, the double diurnal maximum and mini- 

 mum as well as the periodically varying influence of temperature in summer 

 and winter are strikingly apparent. In that of the intensity the morning 

 minimum is the most conspicuous feature, and though the summer and winter 

 inequalities are also perfectly distinct, the daily course of the curves, as Dr. 



