DRIFTING LIGHT- WA VES. 93 



called Plough. I had found reason to feel assured that these 

 five form a system drifting all together amid stellar space. 

 Satisfied for my own part as to the validity of the evidence, 

 I submitted it to Sir J. Herschel, who was struck by its force. 

 The apparent drift of those stars was, of course, a thwart 

 drift; but if they really were drifting in space, then their 

 motions in the line of sight must of necessity be alike. My 

 prediction, then, was that whensoever Huggins applied to 

 those stars the new method he would find them either all 

 receding at the same rate, or all approaching at the same rate, 

 or else that all alike failed to give any evidence at all either 

 of recession or approach. I had indicated the five in the 

 first edition of my " Other Worlds" to wit, the stars of the 

 Plough, omitting the nearest " pointer " to the pole and the 

 star marking the third horse (or the tip of the Great Bear's 

 tail). So soon as Huggins's new telescope and its spectro- 

 scopic adjuncts were in working order, he re-examined Sirius, 

 determined the motions of other stars ; and at last on one 

 suitable evening he tested the stars of the Plough. He 

 began with the nearest pointer, and found that star swiftly 

 approaching the earth. He turned to the other pointer, and 

 found it rapidly receding from the earth. Being under the 

 impression that my five included both pointers, he concluded 

 that my prediction had utterly failed, and so went on with 

 his observations, altogether unprejudiced in its favour, to say 

 the least The next star of the seven he found to be reced- 

 ing at the same rate as the second pointer ; the next at the 

 same rate, the next, and the next receding still at the same 

 rate, and lastly the seventh receding at a different rate. 

 Here, then, were five stars all receding at a common rate, 

 and of the other two one receding at a different rate, the 

 other swiftly approaching. Turning next to the work con- 

 taining my prediction, Huggins found that the five stars thus 

 receding at a common rate were the five whose community 

 of motion I had indicated two years before. Thus the first 

 prediction ever made respecting the motions of the so-called 

 fixed stars was not wanting in success. I would venture to 



