The high latitude, and the winter season of the year rendering but a feeble light at best, the greater the necessity for a more sensitive chemical preparation to the shortening the time for a sitting.

Near the beginning of the year 1841, I discovered and practically applied, chloride of iodine to great advantage, and, as far as memory serves me, I believe the first used in this country was some made and shipped, Messrs.

Harnden & Co., from London, to Mr.Wolcott, in New York.
About the same time, Mr.John Goddard, of London (who was associated with myself), discovered a rather valuable combination of chemicals, consisting of a mixture of iodine, bromine, iodus, and iodic acid, and a proper combination of those bodies gave an action somewhat more sensitive than chloride of iodine--but the "high lights" of the portraits would become solarized or overdone, more frequently with this combination than with the chloride of iodine.

Throughout the year 1841, I used, with great success, chloride of iodine, applied as one coating--occasionally in conjunction with Mr.Wolcott, attempting the use of iodine, bromine, and chlorine, and at times with more or less success.

The difficulty of exactly combining, the three elements above mentioned, in order to produce a certainty of result with harmony of effect, was the work of many months, with great labor and study, the slightest modification requiring a long, series of practical experiments, a single change consuming, frequently, an entire day in instituting comparisons, etc., etc.
Early in the year, 1842, I discovered a combination of chemicals (now known in London as "Wolcott's Mixture," in hermetically sealed bulbs) of exceeding uniform character, very sensitive to the action of light, and specimens produced in 1842-3, with this combination, will bear comparison with the best specimens produced at this late date.
About the same time, I discovered that however much overdone a Daguerreotype might be, the means were at hand to save or redeem it.
It has long, since been known to operators, that if a plate be exposed to light after being coated, unless it be again coated, a clear and distinct picture could not be obtained upon the same plate without first repolishing and recoating the same, care being taken that no light fall upon the prepared surface.