M.uicH 2, 189].] 



KNOWLEDGE. 



49 



sented by rectilinear motion as any other. The proba- 

 bilities, however, in the case of a pair of this kind are 

 greatly in favour of the relative change being due to 

 orbital motion, and it was safe to assume that these stars 

 were far more likely to be physically connected than that 

 one was drifting past the other from proper motion. 



In using the 30-inch telescope for double star work, as 

 far as time would allow, I have looked up and re-measured 

 some of the old pairs which have either been single for 

 many years, or so difficult that they were practically non- 

 measurable with ordinary telescopes. The result has been 

 that in a number of instances a single set of measures of 

 each star made it possible to get a reasonably accurate 

 idea of the periods. In this case, the change in angle 

 since the last measure of Otto Struve amounts to over 

 160°, so that the apparent path of the companion in the 

 future is confined within narrow limits. I had overlooked, 

 when placing this star on the working list, an excellent 

 set of measures by Tarrant in IHHH, made vn.th a 12-inch 

 reflector. These measures are remarkably accordant with 

 my own made with a much more powerful instrument. 



I have taken all the measures of this pair wliich can be 

 used in any investigation of its motion, and laid them ofl' 

 accurately to scale (5 inches=l"), with the distance to the 

 second decimal place, and the angles to the nearest tenth 

 of a degree. As nearly as possible through these positions 

 an ellipse has been drawn which will make the areas 

 proportional to the times, and allow of the minimum 

 correction of the observed angles and distances. The 

 figure shown on the accompanying diagram is in sub- 

 stantial compliance with these conditions, and the errors 

 of observation are practically insensible in measures of 

 this kind. 



The following are the measures made use of : — 



1830 -85 



1840 -50 



1848 -22 



1808 -.50 



1880 -58 



1888 -0!) 



1890 -82 



341-5 

 338-4 

 334 •■'.) 

 329-3 



0"-81 

 0"-74 

 0"-52 

 0"-44 



5 5n 



02 3n 



05 (5 n 



02 10 n 



Certainly single /3 



182--8 0"-3± T 3n 



177''1 0"-29 13 3n 



During the interval of about thirty years, in which 

 there are no measures, it was frequently noted as single, 

 and doubtless was apparently so with the instruments 

 used ; but much of the time the distance must have been 

 at least 0"-2, and of course this would have been noticed 

 with a larger aperture. I have given above my own 

 negative results in 1880, as the observation was made with 

 the l8-;'j-inch of the Dearborn Observatory, and the distance 

 must have been very small to have escaped detection. 

 According to this orbit, at that time the distance should 

 have been a little less than 0"-15, and so slight an elon- 

 gation probably would not have been noticed with that 

 aperture. With the Lick telescope it would have been 

 measureablc at all times. 



It is not claimed that anything more than approximate 

 results can be derived from these investigations, but the 

 graphical method is probably as good as any other with 

 the present data. It is evident that the period is a long 

 one ; and according to this ellipse it would be about 450 

 years. Wo have also the following : — 



Maximum distance - - - 0"-98 

 Minnnum distance - - - 0"-13 (1870) 

 Major axis . . - - l"-55 

 Minor axis ... - 0"-58 

 Position angle of major axis - lC4°-5 

 The change for some time will be mamly in distance. 

 In about five years more it should be 0"-4 ; and it will 



then be easily measurable with almost any instrument. 

 Frequent measures of a pair of this class are not neces- 

 sary. A few careful sets of measures every five or ten 

 years will be all that is required for any purpose. 



Hcttcrs. 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 



HOW DID HE FIND THE WAY ? 

 To the Editor of Kxowledge. 



Dear Sir, — If it will not trespass too greatly on your 

 space, I shoidd be glad if you coidd afford room for the 

 following incident : — 



In August 1889 a gentleman and his family removed 

 from Stockport to St. Leonards-on-Sea, taking with them 

 a fine Tom cat they had had several years. Tom seemed 

 restless at this change of quarters, and, after about a fort- 

 night, disappeared. Some weeks later, Tom's master 

 received a letter from one of his sons who was resident in 

 Stockport to the effect that Tom had been seen by the 

 neighbours prowling round his old home. Shortly after, 

 he disappeared again, and about three weeks later again 

 arrived at St. Leonards in a very dejdorable condition — 

 reduced to a mere skeleton. His master, on returning 

 home late one night, found the cat on the door-step, and 

 was welcomed by him with every possible demoustration 

 of delight. Tom has been very feeble ever since, and is 

 most unwilling to leave the house. 



The puzzle is. how could the cat find his way from 

 St. Leonards t) Stockport, a distance of 200 miles, seeing 

 that he was brought by train, and was shut in a sack for 

 most of the way. And to make the puzzle yet more 

 difficult, the railway journey was necessarily broken in 

 London, and the cat was conveyed from the northern 

 to the southern station in a cab. The return journey to 

 St. Leonards one can understand, but how did he find his 

 way to Stockport "? — E. W. Mavnder. 



[The weak link in this remarkable story seems to be 

 that Tom was only seen and recognised by the neighbours, 

 prowling round his old home. A recognition by tlie son 

 would have been more satisfactory, especially if he had 

 marked Tom. — A. C. Ranyard.] 



I have made inquiries, and find that — 



1. The intimation that the cat had appeared in Stock- 

 port was an independent one, i.e. before the people at 

 Stockport knew that the cat had been missed at St. 

 Leonard's. 



2. The cat was away just over seven weeks in all, and 

 was seen at Stockport during the middle week of the 

 seven. 



3. The cat was seen, recognised, fed, and taken care of 

 by the next-door neighbours of its owners. The son resi- 

 dent in Stockport was unfortunately unable to come to 

 identify the cat until after it had set out on its travels 

 again. 



4. The cat, which was formerly very fine and healthy, 

 has sulfered over since from severe bronchitis. 



5. ^'either the owners of the cat nor the neighbours 

 have the slightest doubt as to its identity. Indeed they 

 are disposed to be rather indignant if it is hinted that 

 there may be the possibility of a mistake. 



If it was not the same cat that turned up at Stockport,, 

 then there certainly were some remarkable coincidences. 



E. \V. M.UTNDER. 



