CELESTIAL MEASURINGS AND WEIGHINGS. 211 



motion was taken account of in the investigation, in a 

 manner we need not here explain. The only other, and 

 in the then state of knowledge a very obvious, way of 

 accounting for it, was to ascribe these anomalous move- 

 ments to the attraction of an unseen companion ; in other 

 words, to consider Sirius as in reality a " double star " 

 its companion being either a non-luminous body, and in 

 the nature rather of a planet than an associated sun ; or, 

 if luminous, so feebly so as to be lost in the rays of Sirius 

 itself, which, in powerful telescopes, is of dazzling bright- 

 ness. Accordingly, Professor Peters, to whom we owe 

 this interesting investigation, proceeded (by steps which 

 we could not possibly make clear to our readers, and 

 which indeed only experts in mathematical calculation 

 can follow) to compute the relative orbit of the pair on 

 the theory- of gravitation, and thence to ascertain, not 

 their mutual distance from each other (for that neces- 

 sarily then remained uncertain) but that of Sirius itself 

 from their common centre of gravity. For this he found 

 an apparent angular measure, of 2"*4, corresponding to 

 about i6J times the distance of the earth from the sun; 

 and calculating on his final result, the observed anoma- 

 lous deviations from uniform rectilinear motion were 

 ' found to be satisfactorily accounted for. 



(37.) It is now time, however, to mention what, to 

 render our explanation more simple, we have hitherto 

 kept out of view, viz., that all the foregoing calculations 

 were directed only to that part of the " proper motion" 

 of Sirius which carries it in the direction of a parallel to 

 the earth's equator, or, as it is technically called, " in 



