Beam of November 17, 1882. 329 



Astronomical Society recently established there, but could not 

 hear of any ; and it is much to be regretted that one from 

 France is all we hear of from that country. 



Upon the foregoing points, Prof. Alexander S. Herschel 

 has very kindly communicated to me, and placed at my dis- 

 posal, some remarks and calculations to the following effect. 

 He considers that the supplied data (the foreign observations 

 had not then been received) all corroborate each other very 

 fairly, the Hewarth (York) observation excepted, which can- 

 not, he thinks, be usefully employed. 



The main body of descriptions serves to track very exactly 

 across the south of England what may be called the shadow- 

 line of the phenomenon thrown by the moon. This is so 

 clearly marked out running magnetic E. and W. from Wood- 

 bridge in Suffolk, across Hungerford in Berks, into Devonshire 

 and Cornwall, that the inclination of the beam's path to the geo- 

 graphical meridian (or, rather, to a parallel of latitude) can be 

 assigned almost exactly. But this average result of the obser- 

 vations will of course bear a little variation according to the 

 amount of confidence that we place, and the changes that we 

 think fit to introduce into the interpretation of some of the 

 descriptions. A line drawn subject to such slight variation 

 will be inclined 24° to the geographical east and west line, 

 which is not only a steeper pitch than the actual magnetic 

 variation (about 20° W.) in the part of England where the 

 shadow-path lay, but, a fortiori, considerably steeper yet than 

 the real slope of magnetic variation in the region of France 

 (about 17° or 18° W.) where the beam really moved, and was 

 shadowed into England. A line inclined at 18° to E. and W. 

 geographical may, however, be drawn along the central eclipse 

 track of the observations, which will do but little violence to 

 them, and represent them nearly, if not quite, as well as the 

 former line. Whichever shadow-route we adopt, persons 

 placed north (and 10° W.) of it in the direction the moon 

 shone to, would see it under the moon at a distance in degrees 

 exactly in proportion to their distance in miles (in that direc- 

 tion) from the shadow-track, or, if placed south of it, over the 

 moon in the same way. To ascertain how many miles of dis- 

 placement in station go to a degree of departure of the object's 

 apparent sky-course above or below the moon, we have only, 

 on the supposition that the same rate of displacement per 

 degree belongs to each of the observations (that is, supposing 

 that all parts of the object's course shadowed by the moon 

 were at one and the same height above the earth, or that its 

 course was really parallel to the earth's surface, or horizontal 

 all the time that it was under observation), to collect all the 



