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Document number: 6914
Date: 05 Feb 1854
Recipient: PARSONS William
Author: TALBOT William Henry Fox
Collection: Birr Scientific and Heritage Foundation / Earl of Rosse Ireland
Last updated: 16th June 2016

Lacock Abbey,
Feb. 5/ 54

Dear Rosse -

Pray give my best thanks for Lady Rosse for her very interesting Specimens of photography - surely there are portions exhibiting the details of the Telescopes which are all that can be desired [missing text or page?] Exhibition in London of Specimens, got up by the photographic society, I am sure it would give them much pleasure to see these specimens if permitted. Would you have any objection to their being exhibited? I mean, the three which represent the telescopes - Of course, I should first have them properly placed in frames & glazed, as all the other specimens are. <1>

To photograph the telescopic image of the moon, is a problem of the highest interest - Very few attempts have yet been made, but one in America was partially successful. I would observe that the winter's cold which now prevails greatly diminishes the Sensibility of all photographic preparations - Have you tried the effect of warming the plate of glass before dipping it in the exciting bath of Nitrate of silver, which latter might be warmed also - Another plan is to have an iron heater behind the plate (moderate heat of course) - it is possible also that radiant heat thrown upon the front or sensitive surface of the plate would answer better. I am about to propose to the Polytechnic institution to get up an experiment of instantaneous photography that can be shown to the Public in a lecture. They possess a great hydroElectric machine capable of giving a powerful Electric flash - it all depends upon that - a small electric battery is not strong enough - It is only the positive image that is visible on the glass for the negative one though necessarily always present, has hitherto escaped observation from its faintness - But it must not be forgotten that this process which succeeds with Electric light, may be inapplicable to the light of the moon which is of a totally different nature - Nothing but Experiment can decide that question.

You mention that with Thomas's Collodion Your 3 feet Speculum gave a tolerably strong impression in 25" I presume this was a negative image, developed with pyrogallic acid - but if you develop with protosulphate or protonitrate of iron, you obtain also a positive image, and this positive is generally ten times more visible than the negative, therefore a positive visible image of the moon ought to be obtained upon collodion in 2" ½ with the 3 feet speculum, and in ½" with the 6 feet speculum - But if the image you obtained in 25" was a positive one, then of course the preceding remarks do not hold good and we have not to look for this acceleration. I look forward with much interest to your future Experiments upon this important subject, the more so that the effect obtained by photography is cumulative in its nature, so that effect invisible to the Eye might be recorded by photography if sufficient time be given for the action of the rays, which of course supposes the object to remain perfectly motionless - a telescope moved by clockwork in a fine Southern climate would probably realise the necessary degree of steadiness in the image

I remain Yours very Truly
H. F. Talbot


Notes:

1. While there is no record of these having been exhibited in London, they were submitted by WHFT to the 1854 Dundee Royal Infirmary Fund Exhibition in Scotland - three views of Lord Rosse's large and small telescope were shown as exhibits 37-39. See Roger Taylor, Photographs Exhibited in Britain 1839-1865; a Compendium of Photographers and Their Works (Ottawa: National Gallery of Canada, 2002).

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