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VIL—NOTES ON THE PHYSICAL APPEARANCE OF THE PLANET 
MARS, AS SEEN WITH THE THREE-FOOT REFLECTOR, AT 
PARSONSTOWN, DURING THE OPPOSITION OF 1877. Br 
JOHN L, E. DREYER, wa, 
WITH PLATES I, AND II, 
[Read February 18th, 1878.] 
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During the opposition of Mars in the Autumn of 1877, the three-foot telescope 
was employed for the examination of the Planet's surface. The six-foot was also 
at first used, principally in the search for the newly discovered satellites, until it 
was found that the glare of the planet was too great to admit of the position of the 
outer one (the only one which could be perceived) being measured by the 
micrometer. The planet’s low altitude at Parsonstown as compared with that at 
Washington will perhaps partly account for this. 
On twenty nights the Planet was examined, but on fifteen only was the steadiness 
and quality of the image considered sufficient to admit of a trustworthy sketch being 
made. ‘Twelve only of these have been considered worthy of being submitted for 
publication, the three others having been made under more unfavourable circum- 
stances. 
The following notes, referring to the several drawings which bear the corres- 
ponding numbers, were made at the time :— 
Puate I. Fig. 1. Sept. 7, 11 50™ Gr. M. T. Power 160 (generally used, sometimes a power of 
215 was applied.) 
», 2. Sept. 8, 11" 0™. Interrupted by clouds several times. 
,», 3. Sept. 8, 11% 50™ (time uncertain). Image very unsteady. 
. Sept. 12, 11* 20" Through clouds; sketch unfinished, but showing all features 
correct. 
5. Sept. 15, 11.35™ Strong fog. 
,, 6. Sept. 16, 10"55™- Definition excellent; details well seen. 
Puate ll. ,, 7. Sept. 17, 10"55™: Definition not good. Moonlight, 
», 8. Sept. 28, 11" 15™ Sky a little hazy. 
», 9. Oct. 1, 10" 55™ Sky a little hazy. 
» 10. Oct. 3. Time? About 11" 10™ Image shaky. 
», Ll. Oct. 8, 9% 40™ Definition not quite satisfactory. 
» 12, Oct. 10, 9" 10" Definition not good ; details not satisfactorily seen. 
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