132 > Altitudes of Mountains, ta’c. visible from 
the angle on the other side of zero, the indices being first pro~— 
perly levelled. Eight readings were thus obtained, and the errors 
of collimation, dividing, &c. reduced to a mere trifle. By this 
method it was also discovered that the instrument being adjusted 
at 52°, the zenith distances would be 10” in defect so soon as 
the thermometer had fallen to 32°, Hence the necessity of 
noting the temperature of the sector at the time of adjusting it, 
and also after every pair of observations. The adjustments, 
which did not require altering more than three or four times in 
the course of the year, are best made at 40° in winter and‘at €0° 
in summer. 
When placed upon a distant object, the cross wires seemed ab- 
solutely to efface it, and to render great accuracy unattainable. 
A filament scarcely visible even in its magnified state, and acci- 
dentally found adhering to the cross wires in the manner exhi- 
bited in Plate II. was successfully substituted, and the point (a) 
considered as the line of vision. 
Before any remarks are made as to the result of the experi- 
ments on terrestrial refraction, it will be proper to state that 
_ twelve observations were made at the observatory in January ; 
thirty-two in February; sixty-one in March; and eighty-six from 
the Ist to the 18th of April; and that the instrument was after- 
wards taken to the following stations: 
Rumbles Moor. 
182]. h. m. h. m. Ther.inshade.Wind. Bar. 
April 23, 7 obs. from 10 20 to 11 30—48 to50 N.E. 
24, 6Go.. ee 17252, 18: 10O—48.. 52 S.S.W. 
25, 24... .. 1045..17 45—60'0. 65 "Es 
28, 6 oe PEO. 22°35 —5 1. 156° W- 
N 
N 
G0 j:38 ool dice! -B0H, 18454 Dosa NG 
and N.N.W. 
June 2, 42... .. 11 5..19380—48 to 63 E.N.E. 
119,281) boon'd. ooo Spy 19 20447..)50°N IN 
Auge FAO agiid 26 M20 pel? 04867959 9S 
Oct. 155 11 we ose 13°15.. 14 20248..50° W. 
Beamsley Rock. 
May 2,33 .. .. 1015..18 0—55to67 S.S.E. . 
June 14, 30 ..  .. 1130..18 30—51.. 64 E.S.E. 26-925 
27, 12... .. 1630..19 50—46..56 N 
Oct. 30, 9... .. 13 5.,.16 25—42..44 WSS. 
Chevin. 
Aug. 13, 37...) .. 11:30to 18 40—57..65 S.S.W. 
