K\f)\\ I.I i)(.i; 



DiXKMHKR. 1912. 



Maks is .1 iiioriiiti); Sl.ir, but pr.ictically invisible. 

 Jl'iMTKR is slill pr.ictic.illy invisible, h.ivint; been in con- 

 junction with the Siiti on neceinber hSth. 



Saturn is an evening Star, 6" South of the Pleiades. Polar 

 seini-diaineter 9". The major axis of the ring is 45j", the 

 minor axis 18}". The ring is now approaching its maximum 

 opening and projects beyond the poles of the planet. 



East clotigations of Tethys (every fourth given). January 

 i" l^-i ,11, 10'' 2" -7 (.', 18" 3" -9 »H, 25" S'-'a c, February 

 2" ()''-4 III. Dione (every third given). January 3" ll''-6 in, 

 n" 4''-6 c, 19" 9''-6 c, 28" 2''-7 m. 



Rhea (every second given). Janu.iry 5" 0''-4 c, 14'' l"-l e 

 23" l^'ge, February 1" 2''-8e. 



For Titan and lapetus, E. W. mean East and West 

 elongations, I. S. Inferior and Superior Conjunction, Inferior 

 being to the North. Superior to the South. Titan, 2" 8"- 1 c I.. 

 6" 4''-0 c W.. 10" 2''-6 e S.. 14" 5''-8 e E., 18" e"-! e I., 

 22"2''-2f W., 26"0''-9f S.. 30"4>'-3 e E. Iapetus9" 8''-2c S , 

 30" 3" -6 HI E. 



Uranus is invisible, being in conjunction with the Sun on 

 the 24th. 



NeI'TUNK is in opposition on the 14th. It enters the map 

 of small stars which was given in " Knowledge " for 

 December, 1911, page 476. 



Meteor Showers tfrom Mr. Uenning's List): — 



Double Stars and Clusters. — The tables of these given 

 last year are again available, and readers are referred to the 

 corresponding month of last year. 



Variable Stars. — Tables of these will be given each 

 month ; the range of R.A. will be made four hours, of which 

 two hours will overlap with the following one. Thus the 

 present list includes R.A. 4*' to S"*, next month 6*' to lO*, and 

 so on. In the case of Algol variables, the time of one 

 minimum is given where possible, and the period. Algol, 

 owing to its brightness, will be given for wider limits. 



Table 54. 



of long period variables o Ceti (Miral will roach a maximum at the end of April, when it will be invisible in the sunshine, but 



it mav be seen brightening earlv in the year. 



NOTES. 



ASTRONOMY. 



By A. C. D. Crommelin, B.A., D.Sc, F.R.A.S. 



POSSIBLE SCREENING ACTION OF MATTER ON 

 GRA\'ITATION.— An article by Professor de Sitter in The 

 Observatory for November describes some recent researches 

 both by him and Herr Bottlinger, of Munich, as to whether 

 any traces can be detected of diminution of the sun's 

 attraction on the moon during the times when she is immersed 

 in the earth's shadow. They both independently found that 

 soiue hitherto imexplained oscillations in her motion, which 

 were brought to light by Professor Newcomb's analysis of the 

 observations, could be explained on this hypothesis; and, 

 further, there were some prospects that the large oscillation 

 with a period of some three centuries, which has hitherto 

 baffled all the elTorts of lunar theorists to find an explanation, 

 might likewise be due to the same action. This last is still 



only a conjecture, but the suggestion seems worthy of further 

 research. The suggestion is by no means a new one ; it was 

 the basis of Le Sage's explanation of gravity by " Ultramundane 

 corpuscles." These were supposed to be tiny atoms flying 

 through all space with inmiense speed, and penetrating the 

 interior of all bodies, meeting, however, some obstruction in 

 doing so ; thus two neighbouring bodies would screen each 

 other to some extent, and each would have a greater bombard- 

 ment on the side away from the other, so that there would be 

 a resultant force pushing the bodies together. 



If the theory is true, many of the fundamental constants of 

 astronomy will need some modification. For example, the 

 nearer portions of an attracting body like the sun will screen 

 the more distant portions, so that the attraction of the latter 

 will be diminished, and its real mass would be somewhat 

 greater than that assumed -. also a sphere would no longer 

 attract as though its mass were concentrated at its centre. 



