JH's account of a comet reminds WT of a strange sighting many years ago. Comments further on improvements in photography, both those made and those needed.

Describes observing of comet that evening.

Comments on confusion between observing comet and zodiacal light. Extensive comments on various materials used in a photographic process where negatives change to positives over long time.

Suggests 'amphitype' as name for JH's process whereby same picture can go from negative to positive. Further comments on comet sighting, and on some improvements to Daguerreotype.

Zodiacal light is a real phenomenon. Further comments on negative to positive process. Questions whether WT can define one cometary orbit with two observations.

Comments on JH's positive calotype. Suggests comet may be return of (J.-D.) Cassini's comet of 1668. Gives theorem for finding parabolic orbit of comet if two observations are made in the ecliptic.

Some comments and questions on mathematics.

Comments and questions about a 'cone of the second order' in mathematics.

Grateful for receipt of JH's Cape Results. Sending photographs by several artists to show that 'knowledge of the art is spreading.'

Thanks for excellent Talbotypes. Notes how few photographs are 'perspective representations on a vertical plane' and suggests how to correct this.

Comments on astronomical symbols, and position of camera when photographing buildings.

Has performed experiments measuring the deviation of spectra through an obliquely placed diffraction grating. Believes they strongly support the wave theory of light.

Refers WT to reference work to check WT's experiments [see WT's 1848-2-4]. JH says he will perform no more experiments in physical optics.

Congratulates JH on appointment to Mastership of Mint. Hopes JH, as member of Cambridge University Commission, will introduce needed reforms.

Appreciates WT's letter of congratulation on JH's appointment [as Master of the Mint, to the Cambridge Commission?]. Has begun work with Cambridge.

Agrees to WT's use of name 'amphitype' [see WT's 1851-5-6 or earlier].

Refers to process which produces pictures that are negative or positive depending upon the light. Hopes to use it to photograph lunar landscape. Wants to call it 'amphitype' if JH agrees.

Wants recommendation from WT for teacher of the 'art of Talbotyping.'

Describes observing solar eclipse at Marienburg in eastern Prussia. Gives advice about whom to see for photography training [see 1851-7-27].

Thanks for examples of WT's photographic engraving; sends a photo in return.