Mr. Macdonald's Observations, &c. 341 
The observations contained in pages 34 8, 347, and 348, 
were taken by applying the magnet-box three times, each 
day, to the meridian. This was, I think, accurately effected, 
by hairs fixed longitudinally on the inside of the box, cor- 
responding with projecting points on the outside. When 
these covered each other, and the meridian, to the eye look- 
ing through a magnifying glass from above, there was a strong 
presumption that the longitudinal axis and o° points of the 
box were on and in the true plane of the meridian. In read- 
ing off, the right hand covered the right eye ; a magnifying 
glass, of a power of was held in the left hand ; the up- 
per axis-hair was brought to cover the o° point ; and the eye, 
hanging over this point, glanced steadily to the left, to read 
off the variation west from south, as the fine minute-scale was 
placed on the flat south end of the needle. This observa- 
tion was taken each time four times, to ensure accuracy. 
Lest, however, any error might have arisen from not placing 
the box accurately in the same situation, in taking the three 
daily observations, two pieces of seasoned wood were fixed 
with wooden pins, nearly parallel to the meridian, on either 
side. The magnet- box was applied to the meridian between 
these, and kept firmly fixed in its position by a number of small 
wooden wedges, urged gently between the box and the lateral 
fixtures. The observations contained in page 349 were taken 
with the magnet thus fixed. A fourth column of observations, 
at various nocturnal hours, is given in page 349. A correspond- 
ing thermometrical observation is attached to each magnetic 
one. The thermometer was placed in the room on the left side 
of my hall. 
It appears from these observations, that the east variation 
