SCIENCE. 



543 



SATELLITES OF MARS. 



DATA FOR EPHEMERIDES OF THE SATELLITES OF MARS IN THE OPPOSITION OF l88l. 



By Professor Asaph Hall. 



Log/ 



F 



Log,? 



G 



PViobos 



u i 



T~) pi m ni; 



9.97946 







296 



3-7 



9.50991 







318 



56.7 



308.50 



234.OI 



9.97948 



296 



2.8 



9.50901 



318 



41.0 



46.18 



84-34 



9.97942 





5-3 



9.50858 



3'° 





143.86 



294 67 



9.97928 



296 



11. 2 



9.50865 



318 



0.1 



241.54 



I44 99 



, 9-979°7 



296 



20.4 



9-50923 



3*7 



34-9 



339.22 



355-32 



" 9-97 8 77 



296 



33,o ' 



9.51037 



317 



7.2 



76.90 



205.65 



9.97839 



296 



49.1 



9-5I205 



316 



36.8 



174-58 



55-97 



9.97792 



297 



8.6 



95I43I 



316 



4-3 



272.26 



206 30 



9-9773 8 



297 



31-4 



9-5I7I5 



315 



30.0 



10.95 



1 16.63 



9.97674 



297 



57-6 



9 52055 



314 



54-3 



107.63 



3 2 6-95 



9 97603 



298 



27.1 



9.52456 



314 



17.8 



205.31 



177.28 



9 975 2 3 



298 



59-7 



9 5 2 9 10 



313 



41.0 



302.99 



27.61 



9-9743S 



299 



35-4 



9.53418 



3i3 



4-3 



40.67 



237.93 



9 9734° 



300 



14.0 



953976 



312 



28.5 



I 3 8 -35 



88.26 



9.97236 



300 



55-3 



9-54578 



311 



S4-o 



236.03 



298.58 



9.97125 



301 



39-o 



9.55218 



311 



21.3 



333- 7 1 



I48 9I 



9.97008 



302 



24.8 



9-55890 



310 



Si 



71.40 



359-24 



9.96886 



303 



12.4 



9 56587 



310 



23.2 



169.08 



209.56 



9-9°759 



304 



i-5 



9.57298 



309 



58.4 



266.76 



59-89 



9 96629 



304 



5i-6 



9.58016 



309 



36-7 



4-44 



270.21 



9.96496 



305 



42.2 



9-58733 



3°9 



18. 1 



102.12 



120.54 



9.96363 



306 



33-° 



9-59-141 



309 



29 



199.80 



330.87 



9.96230 



3°7 



23-4 



9.60131 



308 



So. 6 



297 48 



181. 19 



9.96099 



308 



13.2 



9.60800 



308 



41-3 



35- 16 



3 J -S2 



9-95971 



309 



1.8 



9.61440 



308 



34-6 



132.84 



241.84 



9 95847 



309 



48.8 



9.62047 



308 



3°-S 



230.52 



92.17 



9.95728 



310 



34-o 



9.62618 



308 



28.5 



328.21 



302 50 



9 95614 



3" 



16.9 



9.63149 



308 



28 5 



65.89 



152.83 



9 -95508 



3" 



57-3 



9.63639 



308 



30.0 



163 57 



3-15 



9.95410 



312 



34-8 



9.64084 



308 



32.6 



261.25 



213 47 



Greenw. M. Noon. 

 Date. 



1881 Nov. 



16.0 





18.0 



BDflCEM 



20.0 





22.0 



nunc n) 



'24.0 



B<?y3IF 26.0 





28.0 



• 



30.0 



Dec. 



2.0 





4.0 





6.0 





8.0 





10.0 



mm 



12.0 



* v 



14.0 





16 





18.0 





20.0 



[i 



22.0 





24.0 





26.0 





28.0 





30.0 



1882 Jan. 



1 



3-o 





50 





7.0 





90 





11. 





13.0 



Aberr. 



The angle of position and the distance of the satellite, 

 p and.?, will be computed by the formulas 



s sin / =— f sin (F + it) 

 P 



s cos p — — i g sili (G + »), 



o 



where /'is geocentric distance of Mars. The values of a, 

 and of //, the mean distances and the mean daily motions 

 of the satellites are as follows : 



Deimos. 



a = 32"354i 

 /i = 285°i632 



tang 211 = 



Phobos. 

 a = I2"053l 

 fj — II28 C S405 



The quantity u for each satellite is given for the cor- 

 responding dates in the columns w, and u^. For elonga- 

 tions the value of u is given by the equation 

 f ' 2 sin 2 F + g 3 sin 2 G 

 f* cos 2 F + g* cos 2 G 

 Thus for Dec. 20, u — 325°83 at the elongation, and 

 in the case of Deimos j = 53 7- Near the conjunc- 

 tions this satellite passes within 2"5 of the centre of the 

 planet, and the apparent ellipse will be very eccentric. 

 Calling the brightness of the satelii es unity on October 

 1, 1877, the brightness of the next opposition will be as 

 follows : 



1S81 Nov. 16 brightness = 0.303 

 Dec. 14 " = 0.309 

 1882 Jan. 13 " = 0.330 



The brightness of the satellites on November 16 will 

 be a little greater than when they were last observed 

 with the 1 5-inch refractor of the Harvard College Observa- 

 tory. 



On account of the greater distances of the planet from 

 the Earth and Sun, these satellites will be faint next 

 December, but as the planet will be in declination + 26 , 

 they will be within the reach of several large telescopes, 

 and it is possible that a good series of observations may 

 be obtained. The elongation will occur in the angles of 

 position 68° and 248" nearly, and the satellites should be 

 looked for carefully at such times. 



After the next opposition I hope to unite the observa- 

 tions of 1877, 1879 and 1881 in a new determination of 

 the orbtis. 



U. S. Naval Observatory, Washington, 'June 22, 1881. 



The absorption of ultra-violet rays by certain media is 

 being investigated by M. De Chardonnet. One method 

 adopted is to direct a beam through a liquid in a trough 

 with parallel glass or quartz sides, to Poitevin's photo- 

 chromic paper (which indicates by change of tint, the pres- 

 ence of aclinic rays). In a second method, a solar beam 

 from a heliostat is sent through a slit, an objective of quartz 

 and Iceland spar, and a prism of the spar, to a photo- 

 graphic plate or fluorescent screen ; then a trough half 

 filled with liquid is put before the slit. The author finds 

 that the liquid circulating in plants, or impregnating roots 

 and fruits have all an avidity for chemical rays. Fluores- 

 cence does not seem to be directly related to intensity of 

 actinic absorption ; thus decoction of radish absorbs less 

 than decoction of potatoes, yet the former is without the 

 property, while the latter is not. White wine is weakly 

 fluorescent ; red wine does not fluoresce. Of the few ani- 

 mal liquids examined, blood is found a powerful absorb- 

 ent ; but the aqueous humour of a calf's eye, and the albu- 

 men of eggs, have no action on chemical rays. Distilled 

 water, alcohol, sulphuric ether, collodion, and solution of 

 cane sugar are also inactive. Gelatine intercepts all the 

 chemical rays, and it is sensibly fluorescent. 



