Thanks for JH's suggestions on JT's outline of comet speculations. [G. B.] Airy, too, has replied. Includes more speculations on 'envelopes' and nucleus of comet.

In response to JH's comments on JT's explanation of comets says faintness of head and nucleus does not indicate non-existence; eye may not see all. Experiments with polarized light produce 'gorgeous' 'residual blue.'

Encloses reference to one of JH's letters to JT that has already been printed.

Is delighted with JH's exposition of colors of thin plates and of measurements of a wave of light in Familiar Lectures. Asks permission to quote from it.