Lectures on astronomical theories . ial nature andstated velocity of light for the purpose of examining ontheir own ground that analogy by which the adherentsof the theory suppose it to be supported and demon-strated. ABERRATION. 23 A shower of rain consists of drops of water descendingover an extended area. The drops succeed each othercontinuously for a certain time, and we may assume thatthey all descend at the same angle. But light to whichwe are told to consider the shower of rain analogous,does not descend in a shower of particles or waves overan extended area, but it emanates from a cent
Lectures on astronomical theories . ial nature andstated velocity of light for the purpose of examining ontheir own ground that analogy by which the adherentsof the theory suppose it to be supported and demon-strated. ABERRATION. 23 A shower of rain consists of drops of water descendingover an extended area. The drops succeed each othercontinuously for a certain time, and we may assume thatthey all descend at the same angle. But light to whichwe are told to consider the shower of rain analogous,does not descend in a shower of particles or waves overan extended area, but it emanates from a central pointand radiates from that point in all directions. Nownote the difference as it applies to Herschels of a ball, let A., in the figure, represent a drop ofrain descending perpendicularly towards the point Son the plane. If, as the drop in its descent reachesthe mouth P. of the tube, the tube be supposed tomove in the direction with exactly the requisitevelocity to enable its lower mouth Q. to arrive at simultaneously with the arrival of the drop of rain atthe same point, the drop will have passed through thetube without coming in contact with it. But observethat the upper mouth of the tube will now be at B. Ifa shower of rain be descending, another drop may cer-tainly enter the tube at B. ; but supposing the succes- 24 ABERRATION. sive drops to descend from the one point A. only, andthat their descent is confined to the line , how isa second drop to enter the mouth of the tube which hasadvanced to R. f Yet, would not this be similar to thecase of light emanating from a star. Let the star bedirectly over A. in the line , and let the ray orrays of light enter the mouth of the moving tube, in themanner supposed by Herschel, at P., how are successiverays to enter the mouth of the tube at R. f Rays oflight from the star wiU no doubt arrive at R.; but is itnot evident that they cannot arrive from the star, whichhas remained stationary, at th
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Keywords: ., bookcentury18, bookdecade1870, booksubjectastronomy, bookyear1876
