Expresses reservations about Samuel Brown's work. Apologizes for delay in trying calotype; has done only some vegetable substance trials.

Sends JH samples of his calotypes. Off to Germany on a photographic expedition.

Carl Steinheil has proposed making telescope mirrors by plating silver on glass. Is writing to JH to tell him that somewhat earlier he had included this process in one of his patents.

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.

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.

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.

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

Some comments and questions on mathematics.

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 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.

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

Questions and comments regarding improvements in microscopy.

Comments on several experiments with spectra passing through glass films.

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

Thanks for specimen of light sensitive paper. Provides hint on the chemical process that Louis Daguerre may have used in his photographic work. Sends specimens of JH's own work.

Describes method of varying the size of photographic images. Praises Talbot's light sensitive paper and suggests improvements regarding it. Complains about persons too ready to seek a patent.

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

[Responding to WT's 1826-2-7], JH thanks WT for materials sent, makes suggestions regarding WT's upcoming trip to Geneva, and asks WT to deliver a book to [Alfred] Gautier.