  The thermal structure of a coronal loop, both along and across the loop, is
vital in determining the exact plasma heating mechanism. High resolution
spectroscopic observations of the off-limb corona were made using 25 cm
Norikura coronagraph, located at Norikura, Japan. Observations on a number of
days, were made simultaneously in four forbidden iron emission lines namely,
[Fe XI] 7892 \AA\ line, [Fe XIII] 10747 \AA & 10798 \AA\ lines and [Fe XIV]
5303 \AA\ line and on some days made only in [Fe XI] 7892 \AA\ and [Fe X] 6374
\AA\ lines. Using the temperature sensitive emission line ratios [Fe XIV] 5303
\AA/[Fe XIII] 10747 \AA, and [Fe XI] 7892 \AA/[Fe X] 6374 \AA\ we compute the
electron temperatures along 18 different loop structures observed on different
days. We find a significant negative temperature gradient in all the structures
observed in Fe XIV and Fe XIII and a positive temperature gradient in the
structures observed in Fe XI and Fe X. Combining these results with the
previous investigations by Singh and his collaborators, we infer that the loop
tops, in general, appear hotter when observed in colder lines and colder when
observed in relatively hotter lines as compared to their coronal foot points.
We suggest that this contrasting trend observed in the temperature variation
along the loop structures can be explained by a gradual interaction of
different temperature plasma. The exact mechanism responsible for this
interaction needs further quest and has potential to constrain loop heating
models.
