Dear Sir
The zodiacal light is assuredly no terrestrial phenomenon You will find in Lalande’s Astronomy Art. 844 <1> et seq. <2> a good account of it with abundant references. – It is always best seen in our latitudes at the time of the vernal equinox for reasons there given and as I believe I mentioned in my last, I never recollect to have seen it more characteristically & finely displayed than at the time the comet was first seen here & for a week or 10 days after. Why it is not seen in total eclipses I do not know. The phænomenon is a rare one & people are perhaps not long enough in the dark to enable them to see it. – But there is a certain aureola seen wh may be its central portion.
Will it be giving too much trouble to ask you to look for a certain positive blue photograph of a lady in a chair with a yellow border <3> which I should be glad to have back again & wh seems to have got mislaid among those I sent you. It is my best remaining specimen & I shall have to send it for inspection to one or two more friends. –
No 780 negative blue is done by washing paper with a mixed solution of equal parts Ferro-tartrate of Ammonia (or Ferro-citrate) and Ferro sesquicyanate of Potash (the Red Ferrocyanate).
No 844 is remarkable for having no silver in it – the colouring ingredients being Iron Mercury and Lead. It is connected with a series of singularly complicated and capricious processes tha in which Mercury in its various stages of oxidation plays the leading part (& of which the “Amphitype” <4> is one and not the least puzzling & capricious. It has led me such a dance as I never before was led by any physical enquiry and I have not yet succeeded in reducing it to a definite and certainly successful process giving clear and produceable results, in consequence of which I have not yet published any account of it. – Meanwhile I thank you for your name “Amphitype” which suits it in more ways than you had in view when you suggested it & which I shall certainly adopt for it – in preference to Kelænotype or Allotype.
Your theorem about the comet is interesting – As to the inclination remaining indeterminable it is clear that it must be so, as ex hypothesi both observations being made in the plane of the ecliptic there can be nothing to determine the deviation from that plane. But, since the obsn of a comet in Nodo only determines two lines given in space through which the comets orbit must cut, and the time elapsing between the moments of intersection it would seem to me as if an infinite number of parabolas having the sun for a focus might fulfil these conditions. It is true the lines both lie in one plane & that the focus must be in that plane which is a restriction. Still, I should have hardly expected this to limit the problem to a single solution.
I remain dear Sir Yours very truly
JFW Herschel
H.F. Talbot Esqr
31 Sackville Street
Piccadilly London
[family copy, fair copy]
From … J. F. W. Herschel
To … H. F. Talbot
Dear Sir
The Zodiacal light is assuredly no terrestrial phenomenon. You will find in Lalande’s Astronomy Art. 844 et seq. a good account of it with abundant references. – It is always best seen in our latitudes at the time of the Vernal equinox for reasons there given and as I believe I mentioned in my last, I never recollect to have seen it more characteristically & finely displayed than at the time the Comet was first seen here and for a week or 10 days after Why it is not seen in total eclipses I do not know. The phænomenon is a rare one and people are perhaps not long enough in the dark to enable them to see it. – But there is a certain aureola seen which may be its central portion.
Will it be giving too much trouble to ask you to look for a certain positive blue photograph a lady in a chair with a yellow border which I should be glad to have back again & wh seems to have got mislaid among those I sent you. It is my best remaining specimen & I shall have to send it for inspection to one or two more friends.
No 780 negative blue is done by washing paper with a mixed solution of equal parts – Ferro–tartrate of Ammonia (or Ferro–citrate) and Ferro–sesquicyanate of Potash (the Red Ferrocyanate).
No 844 is remarkable for having no Silver in it – the colouring ingredients being Iron Mercury and Lead. It is connected with a series of singularly complicated and capricious processes in which Mercury in its various stages of Oxidation plays the leading part (and of which the “Amphitype” is one and not the least puzzling & capricious. It has led me such a dance as I never before was led by any physical enquiry and I have not yet succeeded in reducing it to a definite and certainly successful process giving clean and produceable results, in consequence of which I have not yet published any account of it. – Meanwhile I thank you for your name “Amphitype” which suits it in more ways than you had in view when you suggested it & which I shall certainly adopt for it in preference to Kelænotype or Allotype.
I have tried infinite plans for accelerating the Amphitype process in its final stage, but without success. Air & Moisture seem necessary oxidising liquids have no effect– Oxygen gas I have not tried. Chlorine destroys all
Your theorem about the Comet is interesting – As to the inclination remaining indeterminate it is clear that it must be so, as ex hypothesi both observations being made in the plane of the ecliptic there can be nothing to determine the deviation from that plane. But, since the obsn of a comet in Nodo only determines two lines given in space which the comets orbit must cut, and the time elapsing between the moments of intersection it would seem to me as if an infinite number of parabolas having the Sun for a focus might fulfil these conditions. It is true the lines both lie in one plane & that the focus must be in that plane which is a restriction. Still, I should have hardly expected this to limit the problem to a single solution.
I remain Dear Sir
Yours very truly
(Sd) J F W H
I have not heard of Messrs Johnson & Wollcotts improvement in the Daguerrotype & you give no idea of its method or effects.P.S. In the Amphitype a + and – picture coexist in the same paper and may be rendered separately visible. I have specimens in which a + picture is produced on the face and a – one on the back of the thinnest foreign post paper I can get, each visible as such on its own side, and that by one and the same action of light.
Notes:
1. Joseph Jérôme Le Français de Lalande (1732–1807), wrote many treatises on Astronomy, the most well known, Astronomie (Paris: Desaint & Saillant, 1764), was reprinted many times.
2. And following.
3. Probably Herschel’s copy of an engraving, titled ‘positive cyanotype. Aug 17. 1842 JFWH’. NMeM, Bradford, 1943–39/72. See Larry J. Schaaf, Out of the Shadows; Herschel, Talbot & the Invention of Photography (London: Yale University Press, 1992) p. 128.
4. This a reference to the process Herschel originally called Celænotype. In Doc. No: 04784, WHFT suggested that Herschel call his process ‘Amphitype’, which advice Herschel took. Herschel never could resolve this process that led him ‘such a dance’, and he relinquished the name for WHFT’s own use in Doc. No: 06418. The name Amphitype became more widely known as an alternative for direct positives in collodion (ambrotypes).
5. Alexander Simon Wolcott (1804–1844) and John Johnson developed a daguerreotype camera employing a concave mirror rather than a lens. They were granted an American patent, no.1582, 8 May 1840, and 18 March 1843 Wolcott alone was granted a British Patent, no.9672.