Collingwood <1>
March 25/43
My dear Sir
I am somewhat surprised that so many people accustomed to look at physical phænomena should have taken the Comet <2> for a Zodiacal light. – seeing – 1st that its position in the sky was such as the Z.L. never assumes at this season or indeed any other when visible at all 2dly that it was not (to my eyes at least) in the smallest degree resembling that phænomenon being much more concentrated, narrow & of nearly uniform width – & 3dly because at the time of its 1st appearance in the country (17th inst) and every clear night since, the true Zodiacal light has been displayed with a distinctness & brightness I have seldom or never seen equalled thus – [illustration]
Both being visible at the same time, as I said before, I cannot understand how they could be confounded for instance by Sir James South <3> who speaks of an amorphous mass of light to the Northward as if it might be the Comet’s head when it reality it was only the glow of the Zod L seen through among Cloud
Peacock <4> too took the comet on the 17th for the ZL and this morning I have got a letter fr paper from Liverpool in which it is declared that we are all wrong about a comet for it is only a Z.L.! –
If you wish to see the Z.L. in perfection look out the first clear evening when twilight begins to die away
As you wrote to me from abroad mentioning that you were then in personal communicn with M. Steinheil <5> but not giving me any address where I might write to you direct I enclosed to him some specimens of my “Chrysotype” process <6> a pretty pendant to your Kalotype. <7> Since that I have got several very beautiful photographic effects from Mercury, Iron, and Lead, as also by the use of the cyanic compounds, some of which I enclose for your inspection. I must request their return as they form part of a series, which I keep under my eye to watch their slow changes which are very curious and in some cases end in total or almost total obliteration in others with a most remarkable increase of clearness & distinctness. – Nos 1.2.3.4.5. are of this latter class. They are varieties of a process for which I propose to use the name of Celænotype (κελαινος) from the blackness and engraving like effect of some of them. <8> [illegible deletion]
As No 1. They are all originally negative pictures – in some instances of excessive intensity and beautiful sharpness (such as the negative Lady No 8) but in others the negative original impression is so feeble as hardly to be at all discernable. – In this state they may be kept ad libitum but fade more or less rapidly. But whether faded or not, by a certain pickling they are totally obliterated and reduced to the state of white or yellow papers. – In this state also they may be kept – They then undergo a third process which brings out a dirty spoiled positive picture of which No 3 may serve to give some idea, but much worse (No 3 is already in progress to clearing). – They are then laid by in the dark (NB they are fixed) and by very very slow degrees the dinginess goes off the ground clears and leaves a positive picture like No 1 or No 2 as the case may be. For this whole months are requisite. No 2 I believe is complete as for a long while past I have perceived no change in it. – No 1 is not yet fully cleared. No 3 still less so and No 5 hardly at all. – No 4 is a different preparation. It was remarkable when negative for its exceeding intensity & distinctness – Now, lines & streaks before impressioned have come out. I am still working at this process which has led me such a dance as I never before was led by anything in the way of an Expt.
No 10 is a specimen of the positive variety of the “Cyanotype” process described in my paper of wh I sent you a copy during your absence which I hope you received.<9> This also was at first feeble in comparison with what it is and by degrees has assumed also a much bluer colour, having been at first purple then green-blue, in which state, having been till then unfixed it was finally fixed & turned blue by throwing into water.
In none of these specimens does either silver or gold occur – and our Materia Photographica is extending daily. –
I have been lately examining the pure iodurets of mercury and find their photo– and –thermographic properties exceedgy curious. – The perioduret is extremely sensitive to receive a weak impression which fades again almost immediately – By its aid I have produced thermographs of the spectrum on glass by a process which I think throws some light on Moser’s experiments <10> though its details are widely different.
I am very glad to hear you are at work on the improvement of your positive Calotype which after all for travellers anxious to realize their productions, is the more valuable.
What you mention about the Cometic appearance in 1817 is very interesting – I do not doubt that it was the tail of one – And probably such occur oftener than people think. I saw the head of this the evening before last but last night was unsuccessful, – (it seems growing fainter and going away) – unless a nebulous object which I distinctly did see & kept several minutes in the telescope and which lay right in the course of the tail was the comet. – In that case the change in one night was marvelously great.
Believe me My dear Sir yours very truly
JFW Herschel
On the backs of the specimen’s sent you will see which I wish to have returned.
[family copy, fair copy]
Collingwood
March 25 1843
My dear Sir
I am somewhat surprised that so many people accustomed to look at physical phænomena should have taken the Comet for a Zodiacal light.–seeing–1st that its position in the sky was such as the Z. L. never assumes at this season or indeed any other when visible at all 2ndly that it was not (to my eyes at least) in the smallest degree resembling that phenomena being much more concentrated, narrow and of nearly uniform width –& 3rdly because at the time of its 1st appearance in the Country (17th inst.) and every clear night since, the true Zodiacal Light has been displayed with a distinctness & brightness I have seldom or never seen equalled thus…
[diagram of Comet’s path, constellations and of Zodiacal Light, represented by dotted lines]
Both being visible at the same time, as I said before, I cannot understand how they could be confounded for instance by Sir James South who speaks of an Amorphous mass of light to the Northward as if it might be the Comet’s head when in reality it was only the glow of the Zod. L. seen among Cloud. Peacock too took the Comet on the 17th for the Zod. L. and this morning I have got a paper from Liverpool in which it is declared that we were all wrong about a Comet for it is only a Z. L.!
If you wish to see the Z. L. in perfection look out the first clear evening when twilight begins to die away
As you wrote to me from abroad mentioning that you were then in personal commun. with M. Steinheil but not giving me any address where I might write to you direct I enclosed to him some specimens of my “Chrysotype” process a pretty pendant to your Kalotype. Since that I have got several very beautiful photographic effects from Mercury, Iron, and Lead, as also by the use of the Cyanic compounds, some of which I enclose for your inspection, I must request their return as they form part of a series, which I kept under my eye to watch their slow changes which are very curious and in some cases end in total or almost total obliteration in others with a most remarkable increase of clearness & distinctness. – Nos 1.2.3.4.5. are of this latter class. They are varieties of a process for which I propose to use the name of Celænotype (κελαινος) from the blackness and engraving like effect of some of them. as No 1. They are all originally negative pictures – in some instances of excessive intensity and beautiful sharpness (such as the negative Lady No 8) but in others the negative original impression is so feeble at hardly to be at all discernable.– In this state they may be kept ad libitum but fade more or less rapidly. But whether faded or not, by a certain pickling they are totally obliterated and reduced to the state of white or yellow paper.– In this state also they may be kept – They then undergo a third process which brings out a dirty spoiled positive picture of which No 3 may serve to give some idea, but much worse (No 3 is already in progress to clearing).– They are then laid by in the dark (NB they are fixed) and by very very slow degrees the dinginess goes off the ground clears and leaves a positive picture like No 1. or No 2 as the case may be. For this whole months are requisite. No 2 I believe is complete as for a long while past I have perceived no change in it.– No 1 is not yet fully cleared. No 3 still less so and No 5 hardly at all.– No 4. is a different preparation It was remarkable when negative for its exceeding intensity and distinctness – how, lines & streaks before unpercieved [sic] have come out. I am still working at this process which has led me such a dance as I never before was led by anything in the way of an expt
No 10 is a specimen of the positive variety of the “Cyanotype” process described in my paper of wh I sent you a copy during your abscence which I hope you received. This also was at first feeble in comparison with what it is and by degrees has assumed also a much bluer colour, having been at first purple, then green–blue, in which state, having been till then unfixed it was finally fixed & turned blue by throwing into water
In none of these Specimens does either Silver or Gold occur – and our Materia photographica is extending daily.
I have been lately examining the pure iodurets of Mercury and find their photo–and –thermographic properties exceedingly curious.– The perioduret is extremely sensitive to receive a weak impression which fades again almost immediately By its aid I have produced thermographs of the Spectrum on Glass by a process which I think throws some light on Moser’s experiments though its details are widely different.
I am glad to hear you are at work on the improvement of your positive Calotype which after all for travellers anxious to realise their productions, is the most invaluable
What you mention about the Cometic appearance in 1817 is very interesting– I do not doubt that it was the tail of one – and probably such occur oftener than people think. I saw the head of this the Evening before last, but last night was unsuccessful,–(It seems growing fainter and going away)– unless a nebulous object which I distinctly did see and kept several minutes in the telescope and which lay right in the course of the tail was the Comet.– In that case the change in one night was marvellously great
Believe me My dear Sir Yours very truly
(Sd) J. F. W. H.
On the backs of the Specimens sent you will see which I wish to have returned.
Notes:
1. Hawkhurst, Kent.
2. The Great Comet of 1843.
3. Sir James South (1785–1867), astronomer.
4. Prof George Peacock (1791–1858), mathematician.
5. Carl August von Steinheil (1801–1870), astronomer, physicist and optician.
6. A process introduced by Herschel in his paper ‘On the Action of the Rays of the Solar Spectrum on Vegetable Colours, and on some new Photographic Processes’, Philosophical Transactions of the Royal Society of London, 1842, pp. 181–214.
7. Herschel nearly always used this alternative spelling of calotype.
8. In Doc. No: 04784, WHFT suggested that Herschel call his process ‘Amphitype’, which advice Herschel took in Doc. No: 04788. 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).
9. WHFT did in fact receive the offprint, inscribed by Herschel on the title page: “H.F. Talbot Esqr With the Author’s best respects”; it is now in a private collection.
10. Ludwig Ferdinand Moser (1805–1880), physicist and chemist, published De l’acte de la vision, de l’influence de la lumière sur tous les corps et de la lumière invisible in 1842, and Herschel is referring to this work, which he may have known as Moser’s research on Latent Light [see Doc. No: 04541].
11. John David Roberton, assistant Secretary, Royal Society.