XIIL—PHYSICAL OBSERVATIONS OF MARS, 1879-80. ByC. E. BURTON, 
B.A. M.RI.A., F.R.A.S. With Puates, VI., VII., and VIII. 
[Read February 16th, 1880.] 
The series of observations here placed on record embraces a period of three 
months, from Oct. 5, 1879, to January 5, 1880, both days included ; and, as the 
circumstances of observation were on the whole favourable for a careful scrutiny 
of the planet, I now venture to place the results before the Royal Dublin Society. 
Instruments employed.—These were : (1) a 6 inch refractor made and equatoreally 
mounted by Mr. Grubb for my friend, Mr. J. H. Orpin, who has most kindly placed 
his instrument and observatory entirely at my disposal ; (2) and chiefly, an 8 inch 
reflector (Newtonian) with concave specula of home make, mounted as an altazimuth 
on the plan adopted by Mr. John Brett, rr.a.s., and described by him in the 
Monthly Notices of the Royal Astronomical Society, vol. xxxii. p. 294; and, (3) 
a 12 inch Newtonian, also of home manufacture, mounted as an equatoreal. 
The magnifying powers employed varied according to the state of the air from 
220 to 514 diameters, ascertained for each of the instruments by measurement of 
the diameter of the emergent pencil. 
‘The powers found to work best with the reflectors were, for the 8 inch, triple 
achromatic objectives, giving amplifications of 220 and 380 diameters; and for the 
12 inch, single lenses, magnifying respectively 408 and 514 diameters, were 
employed. 
With the 6 inch achromatic, Huyghenian eyepieces yielding the approximate 
powers of 194 and 241 diameters were used, except on Dec. 24, when a new single 
lens eyepiece, magnifying about 270 diameters, was preferred to the equivalent 
Huyghenian. 
Tt was the practice to insert on an outline disk the several details seen, as soon as 
their forms appeared with tolerable distinctness, then to add supplementary sketches 
of each detail on the same paper near to the principal drawing, if further scrutiny 
showed that modifications were necessary. When such supplementary sketches 
were made, the Greenwich mean time of taking each was appended to it. The 
Greenwich mean time of beginning and ending each group of sketches was also 
entered. 
Explanatory notes were added to each sketch, where thought necessary. As 
soon as practicable, these detached sketches with the appended notes were used for 
2¢ 
